Previously we conditionally generated footer->uuid, when libuuid was
available. Now that we have a built-in implementation, we can switch to
it.

Signed-off-by: Fam Zheng <famz@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Jeff Cody <jcody@redhat.com>
Message-Id: <1474432046-325-6-git-send-email-famz@redhat.com>