webadmin:Set highest compatibility version by default in new cluster pop-up

while creating new cluster in Gluster only mode,
the latest version will be selected as Compatibility Version by default

Bug-Url: https://bugzilla.redhat.com/1096646

Change-Id: Iaa76e316b536bedf1b24ce21493716a4b08c9878
Signed-off-by: Karnan <kchidamb@redhat.com>