v2v: -i ova: Fix it so it actually verifies SHA-1 hashes from manifest files.

There were two large bugs before: (1) It only found one manifest file
(meaning that multi-volume OVAs would be broken).  (2) The regular
expression didn't work so it wouldn't check the hash.  Bugs (1) + (2)
combined so that the check just didn't do anything at all, which is
why we didn't notice the multi-volume problem.

Actually I suspect we shouldn't be doing this check at all, since I
bet there are OVAs out there with broken SHA-1's.
tests: v2v: Test -i ova with two input disks.