Move parallel_exec() to exectools; keep only one version

[locriandev]

We have 2 similar functions that are used to execute a given function in a thread pool, with a predefined set of params. These functions are both defined in runtime.Runtime. This PR aims to clean up the code by keeping just one version of parallel_exec; moreover, the natural place for such a function is probably within exectools module.

Tested in a hack space with ocp4-scan, that calls doozer config:scan-sources and parallel_exec: https://saml.buildvm.hosts.prod.psi.bos.redhat.com:8888/job/hack/job/dpaolell/job/ocp4-scan/94/console

[openshift-bot]

Build #1

GLOB sdist-make: /mnt/workspace/jenkins/working/art-tools_doozer_PR-791/setup.py
py38 create: /mnt/workspace/jenkins/working/art-tools_doozer_PR-791/.tox/py38
py38 installdeps: -rrequirements-dev.txt, -rrequirements.txt
py38 inst: /mnt/workspace/jenkins/working/art-tools_doozer_PR-791/.tox/.tmp/package/1/rh-doozer-2.1.1.dev26+g1c0f838.zip
py38 installed: aiofiles==23.1.0,aiohttp==3.8.4,aiosignal==1.3.1,astroid==2.15.5,async-timeout==4.0.2,attrs==23.1.0,autopep8==2.0.2,bashlex==0.18,bcrypt==4.0.1,cachetools==5.3.1,certifi==2023.5.7,cffi==1.15.1,chardet==5.1.0,charset-normalizer==3.1.0,click==8.1.3,colorama==0.4.6,coverage==7.2.7,cryptography==41.0.1,decorator==5.1.1,defusedxml==0.7.1,Deprecated==1.2.14,dill==0.3.6,distlib==0.3.6,dockerfile-parse==2.0.0,exceptiongroup==1.1.2,fastcore==1.5.29,filelock==3.12.2,flake8==6.0.0,flexmock==0.11.3,frozenlist==1.3.3,future==0.18.3,ghapi==1.0.4,gssapi==1.8.2,idna==3.4,iniconfig==2.0.0,isort==5.12.0,jira==3.4.1,koji==1.33.0,krb5==0.5.0,lazy-object-proxy==1.9.0,mccabe==0.7.0,multidict==6.0.4,mysql-connector-python==8.0.33,oauthlib==3.2.2,openshift-client==1.0.19,packaging==23.1,paramiko==3.2.0,platformdirs==3.8.0,pluggy==1.2.0,protobuf==3.20.3,pycodestyle==2.10.0,pycparser==2.21,pydantic==1.10.10,pyflakes==3.0.1,pygit2==1.10.1,PyGithub==1.59.0,PyJWT==2.7.0,pylint==2.17.4,PyNaCl==1.5.0,pyproject-api==1.5.2,pyspnego==0.9.1,pytest==7.4.0,python-dateutil==2.8.2,PyYAML==6.0,requests==2.31.0,requests-gssapi==1.2.3,requests-kerberos==0.14.0,requests-oauthlib==1.3.1,requests-toolbelt==1.0.0,rh-doozer @ file:///mnt/workspace/jenkins/working/art-tools_doozer_PR-791/.tox/.tmp/package/1/rh-doozer-2.1.1.dev26%2Bg1c0f838.zip,semver==3.0.1,setuptools-scm==7.1.0,six==1.16.0,tenacity==8.2.2,tomli==2.0.1,tomlkit==0.11.8,tox==4.6.3,typing==3.7.4.3,typing-extensions==4.7.1,urllib3==2.0.3,virtualenv==20.23.1,wrapt==1.15.0,yarl==1.9.2
py38 run-test-pre: PYTHONHASHSEED='2268615220'
py38 run-test: commands[0] | coverage run --branch --source doozerlib -m unittest discover -t . -s tests/
................................................................................................................................................s.s....................................s.s...s.s...s..s.s.s.................................................................................
----------------------------------------------------------------------
Ran 274 tests in 2.256s

OK (skipped=10)
py38 run-test: commands[1] | flake8
py38 run-test: commands[2] | coverage report
Name                                          Stmts   Miss Branch BrPart  Cover
-------------------------------------------------------------------------------
doozerlib/__init__.py                            12      7      2      1    43%
doozerlib/_version.py                             2      2      0      0     0%
doozerlib/assembly.py                           158     20     87     11    84%
doozerlib/assembly_inspector.py                 220    158    128      8    24%
doozerlib/assertion.py                           13      0      6      0   100%
doozerlib/brew.py                               366    206    152      4    40%
doozerlib/build_status_detector.py               85     10     54      3    86%
doozerlib/cli/__init__.py                       122     64     28      0    39%
doozerlib/cli/__main__.py                      1202   1202    474      0     0%
doozerlib/cli/cli_opts.py                        20      3      8      0    89%
doozerlib/cli/config_plashet.py                 536    536    246      0     0%
doozerlib/cli/config_tag_rpms.py                141     20     77     15    82%
doozerlib/cli/detect_embargo.py                 167     35     70      8    75%
doozerlib/cli/get_nightlies.py                  230     59    127      3    71%
doozerlib/cli/images_health.py                   82     30     26      2    59%
doozerlib/cli/images_streams.py                 687    687    296      0     0%
doozerlib/cli/inspect_stream.py                  66     66     28      0     0%
doozerlib/cli/release_calc_upgrade_tests.py      24     24      6      0     0%
doozerlib/cli/release_gen_assembly.py           277    146    118      3    42%
doozerlib/cli/release_gen_payload.py            703    260    300     20    58%
doozerlib/cli/rpms_build.py                     165     59     58      8    57%
doozerlib/cli/scan_sources.py                   182    141    100      2    17%
doozerlib/comment_on_pr.py                       46      0      8      0   100%
doozerlib/config.py                              97     97     44      0     0%
doozerlib/constants.py                           12      0      0      0   100%
doozerlib/coverity.py                           255    225     82      0     9%
doozerlib/dblib.py                              263    160     68      4    35%
doozerlib/distgit.py                           1456    903    692     40    36%
doozerlib/dotconfig.py                           54     43     31      0    13%
doozerlib/exceptions.py                          14      5      0      0    64%
doozerlib/exectools.py                          226    110     80     10    48%
doozerlib/gitdata.py                            171    137     76      0    14%
doozerlib/image.py                              532    329    232     10    33%
doozerlib/logutil.py                              9      0      2      1    91%
doozerlib/metadata.py                           432    151    184     30    61%
doozerlib/model.py                              113     21     36      2    82%
doozerlib/olm/__init__.py                         0      0      0      0   100%
doozerlib/olm/bundle.py                         315    230     72      0    22%
doozerlib/osbs2_builder.py                      119     30     44     19    67%
doozerlib/plashet.py                            134      9     90     15    89%
doozerlib/pushd.py                               22      0      2      0   100%
doozerlib/release_schedule.py                    28     17      8      0    31%
doozerlib/repos.py                              255     95    123     18    56%
doozerlib/rhcos.py                              248     26     96     15    88%
doozerlib/rpm_builder.py                        232     32    123     32    80%
doozerlib/rpm_delivery.py                        16      1      0      0    94%
doozerlib/rpm_utils.py                          134     23     90     14    81%
doozerlib/rpmcfg.py                             151     61     64      8    55%
doozerlib/runtime.py                            902    686    372      7    18%
doozerlib/source_modifications.py               116     33     26      4    68%
doozerlib/state.py                               23     12      8      0    35%
doozerlib/util.py                               452    217    180     13    48%
-------------------------------------------------------------------------------
TOTAL                                         12287   7388   5224    330    37%
___________________________________ summary ____________________________________
  py38: commands succeeded
  congratulations :)