core: Changed storage type check in ConnectAllHostsToLun command

As a part of the effort to remove the type of storage pool the
StoragerHelper getter in ConnectAllHostsToLun command was change from the
storage pool type to the storage domain type

Change-Id: Ifde05e609e9d7f7a02d6447047a434153770d514
Relates-To: https://bugzilla.redhat.com/1038053
Signed-off-by: Tal Nisan <tnisan@redhat.com>