glusterd : Blocking invalid values for geo-rep config options

Change-Id: Ia9ee44763a9c2798b26d3225bf03a974d7ece21f
BUG: 998962
Signed-off-by: Avra Sengupta <asengupt@redhat.com>
Reviewed-on: http://review.gluster.org/5666
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Amar Tumballi <amarts@redhat.com>
Reviewed-by: Venky Shankar <vshankar@redhat.com>
Reviewed-by: Vijay Bellur <vbellur@redhat.com>