Makes popper independent of .git

[JayjeetAtGithub]

Addresses #665, #647

[pep8speaks]

Hello @JayjeetAtGithub! Thanks for updating this PR. We checked the lines you've touched for PEP 8 issues, and found:

There are currently no PEP 8 issues detected in this Pull Request. Cheers! 🍻

Comment last updated at 2019-06-04 09:17:26 UTC

[JayjeetAtGithub]

@ivotron When we return "" from scm.get_sha() method, then in this line in gha.py, the tag variable in docker runner remains incomplete and throws error due to self.env['GITHUB_SHA'] being empty. With what should we replace the return value to handle this situation ?

[JayjeetAtGithub]

@ivotron Can you please tell me what would be the best way to run all the tests with and without .git ?
I have achieved it by setting an env variable POPPER_TEST_MODE and changing the init_test_repo body in ci/test/common depending on the env vars value.

[JayjeetAtGithub]

@ivotron Should we fail or warn on finding a detached head? Means I want to know whether it is ok to have a detached head. Currently, I check for a detached head in init_repo_object in scm.py and fail if one is found. This line puts the head in detached state and build fails. How to deal with this ? Thanks

[JayjeetAtGithub]

@ivotron Made the changes. I called check_if_detached_head from scm.py in CI env because if I would call it through gha.py, I would naturally skip the check when using the scm functions separately, like in the get_head_commit(), etc and run into error.

[ivotron]

thanks a lot!