init: add systemd service files

This patch adds systemd service files. It is possible to start and
enable multiple instances (per monid, osdid, mds name), e.g.

 # systemctl start ceph-mon@node01
 # systemctl enable ceph-mon@node01

 # systemctl start ceph-osd@0
 # systemctl enable ceph-osd@0

The ceph cluster can be set in the system config file:

 /etc/sysconfig/ceph

adding or editing the CLUSTER environment variable.

Signed-off-by: Federico Simoncelli <fsimonce@redhat.com>