ceph-disk: reimplement is_partition

Previously we were assuming any device that ended in a digit was a
partition, but this is not at all correct (e.g., /dev/sr0, /dev/rbd1).
Instead, look in /dev/disk/by-id and see if there is a symlink that ends in
-partNN that links to our device.

There is probably still a better way...

Signed-off-by: Sage Weil <sage@inktank.com>
ceph-disk: reimplement list_all_partitions

Use /dev/disk/by-id to list disks and their partitions.  This is more
accurate and correct than the previous (as-yet unused) implementation.

Signed-off-by: Sage Weil <sage@inktank.com>
ceph-disk: implement 'list'

This is based on Sandon's initial patch, but much-modified.

Mounts ceph data volumes temporarily to see what is inside.  Attempts to
associated journals with osds.

Resolves: #3120
Signed-off-by: Sage Weil <sage@inktank.com>