build/glusterfs.spec.in: %post server doesn't wait for old glusterd

'killall glusterd' needs to wait for the old glusterd to exit
before starting the updated one, otherwise the new process can't
bind to its socket ports

Change-Id: Ib43c76f232e0ea6f7f8469fb12be7f2b907fb7c8
BUG: 1113543
Signed-off-by: Kaleb S. KEITHLEY <kkeithle@redhat.com>
Reviewed-on: http://review.gluster.org/8185
Reviewed-by: Niels de Vos <ndevos@redhat.com>
Reviewed-by: Lalatendu Mohanty <lmohanty@redhat.com>
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Humble Devassy Chirammal <humble.devassy@gmail.com>
Reviewed-by: Vijay Bellur <vbellur@redhat.com>