vhdx: Use QEMU UUID API

This removes our dependency to libuuid, so that the driver can always be
built.

Similar to how we handled data plane configure options, --enable-vhdx
and --disable-vhdx are also changed to a nop with a message saying it's
obsolete.

Signed-off-by: Fam Zheng <famz@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Jeff Cody <jcody@redhat.com>
Message-Id: <1474432046-325-4-git-send-email-famz@redhat.com>