This change adds functionality to allow the ceph osd cluster to
upgrade in a serial rolled fashion.  This will use the ceph monitor
cluster to lock and allows only 1 ceph osd server at a time to upgrade.
The upgrade is initiated setting a config value for source for the
service which will prompt the osd cluster to upgrade to that new
source and restart all osds processes server by server.  If an osd
server has been waiting on a previous server for more than 10 minutes
and hasn't seen it finish it will assume it died during the upgrade
and proceed with its own upgrade.

I had to modify the amulet test slightly to use the ceph-mon charm
instead of the default ceph charm.  I also changed the test so that
it uses 3 ceph-osd servers instead of 1.

Limtations of this patch: If the osd failure domain has been set to osd
than this patch will cause brief temporary outages while osd processes
are being restarted.  Future work will handle this case.

Change-Id: Id9f89241f3aebe4886310e9b208bcb19f88e1e3e