ceph-disk: consolidate ceph-disk-* into a single binary

 ceph-disk prepare ...
 ceph-disk activate ...
 ceph-disk ...

This let's us share code (we were already duplicating a bunch of stuff!)
and to add new commands easily.

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

Use a single exception type, and catch it at the top level.

Signed-off-by: Sage Weil <sage@inktank.com>
ceph-disk: simplify command dispatch

Signed-off-by: Sage Weil <sage@inktank.com>
ceph-disk: install and package

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