blockresize: Skip the qed test if not supported.

1) Skip the qed test for newer libvirt who don't support this format.

2) Fix raw checking math to fix an error.

Signed-off-by: Hao Liu <hliu@redhat.com>
Merge pull request #284 from Hao-Liu/fix_blockresize

blockresize: Skip the qed test if not supported.