savevm: Delete snapshots just created in case of error

bdrv_all_create_snapshot() can fails with some snapshots created,
so it's better to delete those snapshots before returns to the caller

Signed-off-by: Tuguoyi <tu.guoyi@h3c.com>
Message-Id: <1607410416-13563-3-git-send-email-tu.guoyi@h3c.com>
Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>

migration/savevm.c

@@ -2833,6 +2833,7 @@ int save_snapshot(const char *name, Error **errp)
     if (ret < 0) {
         error_setg(errp, "Error while creating snapshot on '%s'",
                    bdrv_get_device_or_node_name(bs));
+        bdrv_all_delete_snapshot(sn->name, &bs, NULL);
         goto the_end;
     }