[Libguestfs] [PATCH v2] v2v: ova: Don't rely on qemu-img version, test "offset"

[Richard W.M. Jones]

v1 -> v2:

- Use 'qemu-img info' which avoids one of the temporary files
  (thanks Tomáš).

- Add a unit test.

Unfortunately when I run 'make -C v2v check' I don't think this code
is being run at all, so there may be something else going on here
which I don't understand.

Rich.