Remove '.git/hooks/post-checkout' hooks when using fetch strategy

This is a general Merge Request template. Consider to choose a template from the list above if it will match your case more.

What does this MR do?

Removes .git/hooks/post-checkout hook which could be create on previous job. Usable when using fetch strategy.

Why was this MR needed?

Please read #2245 (closed) (especially https://gitlab.com/gitlab-org/gitlab-ci-multi-runner/issues/2245#note_30792147) for a reference

Are there points in the code the reviewer needs to double check?

Does this MR meet the acceptance criteria?

• Documentation created/updated
• Tests
  • Added for this feature/bug
  • All builds are passing
• Branch has no merge conflicts with master (if you do - rebase it please)

What are the relevant issue numbers?

Closes #2245 (closed)

approved this merge request

@tmaczukin Should we document that behaviour of clone? Can someone be surprised by it?

Hmmm, yeah, it make sense. But where should we document it? In Runner's documentation (if yes, then in which section)? Or in GitLab's documentation? We don't have any documentation describing how job uses Git, only few places where we describe configuration options. Maybe it should be created and added as a new entry to https://docs.gitlab.com/ce/ci/#advanced-use? There we could describe that when using fetch strategy we're deleting the post-checkout hook. Or should we just add this to the description of GIT_STRATEGY?

I wonder if the better way would not be to specify: core.hooksPath to path outside of repository?

And revert that change after executing git commands?

merged