qcow2: Fix BDRV_O_INACTIVE handling in qcow2_invalidate_cache()

qcow2: Fix BDRV_O_INACTIVE handling in qcow2_invalidate_cache()

What qcow2_invalidate_cache() should do is close the image with
BDRV_O_INACTIVE set and reopen it with the flag cleared. In fact, it
used to do exactly the opposite: qcow2_close() relied on bs->open_flags,
which is already updated to have cleared BDRV_O_INACTIVE at this point,
whereas qcow2_open() was called with s->flags, which has the flag still
set. Fix this.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>