mc rb --force minio/my-bucket should be idempotent

[binaryfire]

Similar to #4863

In Linux, using the force flag when removing directories (rm -rf) doesn't throw an error if the directory doesn't exist. This is by design: -rf is the equivalent of saying "just make sure the directory doesn't exist". That allows it to be used idempotently in scripts.

Similarly I think the --force flag in mc rb --force minio/my bucket should make the command idempotent. Instead of exiting with an exit code of 1 and mc: <ERROR> Unable to validate target 'minio/my-bucket'. Bucket 'my-bucket' does not exist message, it would be better if the exit code was 0 and a simpler informational message like mc: Bucket 'my-bucket' does not exist was shown.