backport ceph-disk to dumpling 

To get the fix for 7334 to dumpling it was safer to backport all the recent work on ceph-disk that makes it safer to run system commands regardless of the path.

This PR backports all the ceph-disk commits, syncing dumpling with current master. 

There is only one commit that had to be bisected and is duly noted on the commit message with the hash of the original commit so that it can be backtracked.