Replace calls of old bdrv_open

Replace calls of old bdrv_open

What is known today as bdrv_open2 becomes the new bdrv_open. All remaining
callers of the old function are converted to the new one. In some places they
even know the right format, so they should have used bdrv_open2 from the
beginning.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>