Provide a block encryption implementation that follows the
LUKS/dm-crypt specification.

This supports all combinations of hash, cipher algorithm,
cipher mode and iv generator that are implemented by the
current crypto layer.

There is support for opening existing volumes formatted
by dm-crypt, and for formatting new volumes. In the latter
case it will only use key slot 0.
Reviewed-by: NEric Blake <eblake@redhat.com>
Signed-off-by: NDaniel P. Berrange <berrange@redhat.com>