fix: make asdf latest output consistent

[cj81499]

Summary

Modify the default query used by asdf latest to allow for "v" prefixes.

Additionally, perform a small refactor to extract some duplicated logic to a helper function.

Fixes: #1684

Other Information

I believe that asdf latest --all uses an empty query (it simply doesn't pass a query argument), which is different than asdf latest <plugin>.
I think both should use the same default query, but I'm not sure which ("v?[0-9]" vs "") should be preferred. I'd like guidance on which should be preferred.

[cj81499]

I'm having trouble reproducing the test failures locally (in fact, I'm having trouble getting a clean run of the tests on the default branch).

I'd appreciate help getting the tests running/passing.

[hyperupcall]

The tests that usually fail are in update_command.bats. When I run bats test, 5 tests fail out of 368:

update_command.bats
 ✓ asdf update --head should checkout the master branch
 ✗ asdf update should checkout the latest non-RC tag
   (in test file test/update_command.bats, line 41)
     `[ "$status" -eq 0 ]' failed
   Cloning into '/tmp/asdf.UZh0/home/.asdf'...
   done.
 ✗ asdf update should checkout the latest tag when configured with use_release_candidates = yes
   (in test file test/update_command.bats, line 54)
     `[ "$status" -eq 0 ]' failed
   Cloning into '/tmp/asdf.OpSy/home/.asdf'...
   done.
 ✓ asdf update is a noop for when updates are disabled
 ✓ asdf update is a noop for non-git repos
 ✓ asdf update fails with exit code 1
 ✗ asdf update should not remove plugin versions
   (in test file test/update_command.bats, line 85)
     `[ "$status" -eq 0 ]' failed
   Cloning into '/tmp/asdf.RWrB/home/.asdf'...
   done.
 ✗ asdf update should not remove plugins
   (in test file test/update_command.bats, line 95)
     `[ "$status" -eq 0 ]' failed
   Cloning into '/tmp/asdf.dOCk/home/.asdf'...
   done.
 ✗ asdf update should not remove shims
   (in test file test/update_command.bats, line 106)
     `[ "$status" -eq 0 ]' failed
   Cloning into '/tmp/asdf.n4EO/home/.asdf'...
   done.

If you get other failures that aren't due to your changes, it might be useful to file an issue about that.