Suppressed inappropriate warning with GitClone

When intentionally suppressing GitClone to
prevent redundant safety clones, bloom was
previously printing warnings which indicated that
the safety mechanisms were disabled. Now it does
not. I also fixed the usage of GitClone between
bloom-release and git-bloom-release.
Merge pull request #159 from ros-infrastructure/issue_159

Suppress warnings about transactional safety when running bloom-release