Implement HTTP POST based RPC (#5840)

Added support for new RPC support using HTTP POST.  RPC's 
arguments and reply are Gob encoded and sent as HTTP 
request/response body.

This patch also removes Go RPC based implementation.

cmd/jwt.go

@@ -136,3 +136,10 @@ func webRequestAuthenticate(req *http.Request) error {
 	}
 	return nil
 }
+
+func newAuthToken() string {
+	cred := globalServerConfig.GetCredential()
+	token, err := authenticateNode(cred.AccessKey, cred.SecretKey)
+	logger.CriticalIf(context.Background(), err)
+	return token
+}