Btrfs-progs: add a message to know zero log ran successfully

If there are errors when opening the fs because of PARTIAL we could think that
the zero-log didn't actually work.  Add a printf so we know that it was
successfull.  Thanks,

Signed-off-by: Josef Bacik <jbacik@fb.com>
Signed-off-by: David Sterba <dsterba@suse.cz>

btrfs-zero-log.c

@@ -71,6 +71,7 @@ int main(int ac, char **av)
 	btrfs_set_super_log_root_level(root->fs_info->super_copy, 0);
 	btrfs_commit_transaction(trans, root);
 	close_ctree(root);
+	printf("Log root zero'ed\n");
 out:
 	return !!ret;
 }