Merge pull request #6926 from dachary/wip-14080-ceph-disk-udevadm

ceph-disk: fix failures when preparing disks with udev > 214

On CentOS 7.1 and other operating systems with a version of udev greater or equal to 214,
running ceph-disk prepare triggered unexpected removal and addition of partitions on
the disk being prepared. That created problems ranging from the OSD not being activated
to failures because /dev/sdb1 does not exist although it should.

Reviewed-by: Sage Weil <sage@redhat.com>