rbd: Close image in qemu_rbd_open() error path

Commit e2b8247a introduced an error path in qemu_rbd_open() after
calling rbd_open(), but neglected to close the image again in this error
path. The error path should contain everything that the regular close
function qemu_rbd_close() contains.

This adds the missing rbd_close() call.
Signed-off-by: NKevin Wolf <kwolf@redhat.com>
Reviewed-by: NEric Blake <eblake@redhat.com>

block/rbd.c

@@ -787,6 +787,7 @@ static int qemu_rbd_open(BlockDriverState *bs, QDict *options, int flags,
                          "automatically marking the image read-only.");
             r = bdrv_set_read_only(bs, true, &local_err);
             if (r < 0) {
+                rbd_close(s->image);
                 error_propagate(errp, local_err);
                 goto failed_open;
             }