DNM: ceph-disk: run partprobe after zap

Not running partprobe after zapping a device can lead to the following:

* ceph-disk prepare /dev/loop2
* links are created in /dev/disk/by-partuuid
* ceph-disk zap /dev/loop2
* links are not removed from /dev/disk/by-partuuid
* ceph-disk prepare /dev/loop2
* some links are not created in /dev/disk/by-partuuid

This is assuming there is a bug in the way udev events are handled by
the operating system.

http://tracker.ceph.com/issues/9665 Fixes: #9665

Signed-off-by: Loic Dachary <loic-201408@dachary.org>