webadmin: Fix allocation policy and storage domain when editing VM disk

Edit Vm disk window always displayed disk allocation policy based on the
storage type instead of displaying the actual allocation policy of that
disk.
In case of the storage domain, first domain from the list of available
storage domains was displayed instead of the storage domain of that disk.

Change-Id: Ifae8052b4e37a7ad7f39eb38081268a7b6bd1a43
Bug-Url: https://bugzilla.redhat.com/1057622
Signed-off-by: Sergey Gotliv <sgotliv@redhat.com>