Enforce signature v4 tests all the time, server defaults to only authenticated requests.

All requests must be authenticated to minio server from now on by using keys generated at
``${HOME}/.minio/users.json`` - from ``minio controller`` during its first time run.

Add a new hidden option ``--anonymous`` for running server in unauthenticated mode.

flags.go

@@ -49,6 +49,12 @@ var (
 		Usage: "Limit for total concurrent requests: [DEFAULT: 16].",
 	}
 
+	anonymousFlag = cli.BoolFlag{
+		Name:  "anonymous",
+		Hide:  true,
+		Usage: "Make server run in anonymous mode where all client connections are accepted.",
+	}
+
 	certFlag = cli.StringFlag{
 		Name:  "cert",
 		Usage: "Provide your domain certificate.",