add a key for ceph-deploy-branch detection

Signed-off-by: Alfredo Deza <alfredo@deza.pe>
safer fallback. Updates docstring

Signed-off-by: Alfredo Deza <alfredo@deza.pe>
remove fallback of the fallback. so silly

Signed-off-by: Alfredo Deza <alfredo@deza.pe>
Merge pull request #28 from alfredodeza/5887

Allow a user to define a ceph-deploy branch to use (instead of master)