contrib: Add systemd unit file

Change-Id: Ia9f6b9cb3212f7e1c05e3cf4408558859a92c963
Signed-off-by: Adam Litke <alitke@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/22931
Reviewed-by: Sandro Bonazzola <sbonazzo@redhat.com>