Blender Git Loki

Codesign: Implement buildbot worker side DMG bundling

Is based on bundle.sh but is adopted to an environment where
codesigning is happening in a dedicated VM.

Also fixed some code from previous commits:

- Removed debug only early output when running commands
- Ensured that path to git is always valid
(wasn't a case when __file__ is relative to current directory).
- Fixed simple code signer which couldn't have imported util.