Make git init to be quiet

What does this MR do?

Related to https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/28642.

Currently, Runner does generate a \section_begin with:

[0Ksection_start:1558614792:get_sources
[0KReinitialized existing Git repository in /builds/gitlab-org/gitlab-ce/.git/
[32;1mFetching changes with git depth set to 20...[0;m

This makes the information in section to first start with Fetching changes, and move Init/Reinit after that.

[0Ksection_start:1558614792:get_sources
[32;1mFetching changes with git depth set to 20...[0;m
[0KReinitialized existing Git repository in /builds/gitlab-org/gitlab-ce/.git/

Why was this MR needed?

Make build log nicer.

Does this MR meet the acceptance criteria?

• Documentation created/updated
• Added tests for this feature/bug
• In case of conflicts with master - branch was rebased

What are the relevant issue numbers?