mount: Added the xlator-option to mount.glusterfs script.

Now all xlator-options can be set from the mount command as well.
Example :
mount -t glusterfs Hostname:/Volume_Name Mount_Point -o "xlator-option=xyz=123, xlator-option=abc=999"

Change-Id: If52d994986839d1c969e3e2e01b2e1a29a3140b7
BUG: 920583
Signed-off-by: Avra Sengupta <asengupt@redhat.com>
Reviewed-on: http://review.gluster.org/4660
Reviewed-by: Amar Tumballi <amarts@redhat.com>
Reviewed-by: Shishir Gowda <sgowda@redhat.com>
Reviewed-by: Jeff Darcy <jdarcy@redhat.com>
Tested-by: Gluster Build System <jenkins@build.gluster.com>