glusterd: Added validation function for quota-timeout.

Change-Id: I7f82f4217a41e0fe41272e6ef82925e1fe97fcd5
BUG: 765230
Signed-off-by: Avra Sengupta <asengupt@redhat.com>
Reviewed-on: http://review.gluster.org/4557
Reviewed-by: Amar Tumballi <amarts@redhat.com>
Tested-by: Gluster Build System <jenkins@build.gluster.com>