ceph.spec.in: Standardize systemd preun and postun scripts

ceph.spec.in: Standardize systemd preun and postun scripts

Currently, the main ceph package and the ceph-radosgw behave
differently on upgrade. This commit unifies their behavior
to the following:

On package removal, disable and stop all related systemd units.

On package upgrade, do nothing unless there is a file /etc/sysconfig/ceph
containing a parameter CEPH_AUTO_RESTART_ON_UPGRADE. If parameter is set
to "yes", restart the systemd units iff they are running.

Signed-off-by: Nathan Cutler <ncutler@suse.com>