webadmin: On new disk creation update wipe after delete on storage change

In new disk dialog the wipe after delete property determined by the default
storage domain that was selected, since a data center can now consist of
storage domain of different storage types, the wipe after delete property
should be update upon change in the storage domain to reflect the correct
behavior that fits the selected storage domain type

Change-Id: Icefd405217fd7498d911809ca02f0f7cf7b42f24
Signed-off-by: Tal Nisan <tnisan@redhat.com>
Bug-Url: https://bugzilla.redhat.com/1063935