packaging: spec: use systemd macros
packaging: spec: use systemd macros

Use systemd macros which are available since Fedora 18
and are available in EL7 as well.
Dropped calls to systemctl reload where not needed.

Change-Id: If5bc3cbdc9845f2638649eb88ed53d88351f08b5
Signed-off-by: Sandro Bonazzola <fcb014d63786651910af5db2ecc5316c668188ef@redhat.com>

oVirt/ovirt-guest-agent,oVirt/ovirt-guest-agent,oVirt/ovirt-guest-agent,oVirt/ovirt-guest-agent