- We expect destroy to fail in zfs_clone() so try to silence it so users are
  not irritated when they create zfs snapshots.
- Add -r recursive to zfs_destroy(). This code is only hit when a) the
  container has no snapshots or b) the user calls destroy with snapshots. So
  this should be safe. Without -r snapshots will remain.
Signed-off-by: Christian Brauner <christian.brauner@canonical.com>