Move bdrv_is_read_only() up with its friends.

Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: John Snow <jsnow@redhat.com>
Signed-off-by: Jeff Cody <jcody@redhat.com>
Message-id: 73b2399459760c32506f9407efb9dddb3a2789de.1491597120.git.jcody@redhat.com