qa_crowbarsetup: Allow bind mounts for local repos

Optionally use local bind mounts instead of nfs when local repositories
should be used.
qa_crowbarsetup: Local repos handling for Cloud

Add local repository support for the cloud iso image.
qa_crowbarsetup: Cleanup repositories

If local repositories are used, cleanup all available repositories so no
remote repos are used.
qa_crowbarsetup: Restructure sles repos handling

Move SLES repository handling to single function and add local
repository support.