webadmin: Disable select quota on edit vm-pool

Quota selection was enabled on edit vm-pool dialog (unlike all other
fields).

set the quota selection box to disabled.

Change-Id: Ifebe28c31bf7f8a5320b70aa62f6eba733333b6c
Bug-Url: https://bugzilla.redhat.com/966003
Signed-off-by: Ofri Masad <omasad@redhat.com>