ansible/minio_configure: allow attaching policies to fail

Attaching a policy to a user/group will fail if the policy is already attached, which is why I first decided to delete the user/group before re-creating it.

This was however not a foolproof solution, as removing a group doesn't work if some users are in it... which may happen when minio crashes while running some jobs.

So, rather than trying to inspect the internal state of MinIO, let's just duplicate what they did upstream1 (just ignore the error), and be done with it.