qcow2: Check that corrupted images can be repaired in iotest 060

We just fixed a few bugs that caused QEMU to crash when trying to
write to corrupted qcow2 images, and iotest 060 was expanded to test
all those scenarios.

In almost all cases the corrupted images can be repaired using
qemu-img, so this patch verifies that.

Signed-off-by: Alberto Garcia <berto@igalia.com>
Message-id: 0b1b95340ecdfbc6927e36adf2fd42ae6198747a.1510143008.git.berto@igalia.com
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Max Reitz <mreitz@redhat.com>