build: sync glusterfs.spec.in with Fedora glusterfs.spec

* fix the hardening fix for shlibs
* use %{__sed} macro
* better short ChangeLog
* fix hard-coded path in extras/systemd/glusterd.service in, use @prefix@

Change-Id: I267244b68a97cbcd6f6ab62fc322c78db45023bb
BUG: 950083
Signed-off-by: Kaleb S. KEITHLEY <kkeithle@redhat.com>
Reviewed-on: http://review.gluster.org/5264
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Niels de Vos <ndevos@redhat.com>