core,webadmin: Move storage type checks to domain instead of pool

As a part of the effort to remove the type of storage pool, checks of the
storage type are changed to check the type on the storage domain instead of
the storage pool

Change-Id: I3db80f1749d93444e9cdac8038859b7d0865f6e5
Relates-To: https://bugzilla.redhat.com/1038053
Signed-off-by: Tal Nisan <tnisan@redhat.com>