glusterd/cli: Updated the options descriptions for "volume set help"

Change-Id: I0db00b7334bb9707ab48bd661ac03a3ad818d6e4
BUG: 893458
Signed-off-by: Avra Sengupta <asengupt@redhat.com>
Reviewed-on: http://review.gluster.org/4393
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Anand Avati <avati@redhat.com>