Don't label or format disks for Ceph OSDs

Along with the changes from this https://github.com/Mirantis/fuel/pull/773
we no longer need to label Ceph disks. This removes superflous mkfs calls during
post-intallation and works around issues in ceph-deploy and ceph-disk.
Closes-Bug: #1246513

Change-Id: I91e6c253c164936c8b12798520cbd45587a36036
Merge "Don't label or format disks for Ceph OSDs"