init-ceph: kick off ceph-create-keys when starting mons

We don't have a particularly tidy way to kick off ceph-create-keys from
sysvinit.  So, do something simple, ugly, and functional: if we are
starting a mon, and it looks like a 'new' type that is in /var/lib/ceph,
then start ceph-create-keys too.

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