MDLSITE-2009 Clarify paths

1st commit:
- Ensure that gitmirror exists.
- Ensure all operations happen there.

2nd commit:
- Ensure that stable branches are processed from older to newer. 

3rd commit:
- integration.git is named "origin" within gitmirror 

4th commit:
- prevent orphaned line to be executed as separate command. Comments break continuous, apparently.