debian: make ceph depend on ceph-common >= 0.67

The older versions of ceph-common (ceph CLI, in particular) can't talk to
newer clusters.  The primary change happened with dumpling when the new
CLI and rest-api changes were made.  Although in reality ceph doesn't
care what version of ceph-common is installed, in practice this forces
ceph-common to get upgraded along with ceph and avoids some user pain.

Fixes: #7641
Signed-off-by: Sage Weil <sage@inktank.com>