Failing centos 7 dokken tests in the CI

[artem-sidorenko]

Describe the bug
CentOS 7 tests in dokken fail in the CI due to selinux testing

Expected behavior
CentOS 7 dokken tests should run properly in the CI

Actual behavior
https://travis-ci.org/dev-sec/chef-os-hardening/jobs/517959153

Additional context
The problem is due to selinux_enabled test suite in the .kitchen.yml. This suite gets executed for dokken testing too and the tests are failing due to missing selinux tools. We should exclude this suite from be executed within dokken