Adopt dsync interface changes and major cleanup on RPC server/client.

* Rename GenericArgs to AuthRPCArgs
* Rename GenericReply to AuthRPCReply
* Remove authConfig.loginMethod and add authConfig.ServiceName
* Rename loginServer to AuthRPCServer
* Rename RPCLoginArgs to LoginRPCArgs
* Rename RPCLoginReply to LoginRPCReply
* Version and RequestTime are added to LoginRPCArgs and verified by
  server side, not client side.
* Fix data race in lockMaintainence loop.

cmd/utils_test.go

@@ -232,6 +232,12 @@ func TestLocalAddress(t *testing.T) {
 	if runtime.GOOS == "windows" {
 		return
 	}
+
+	currentIsDistXL := globalIsDistXL
+	defer func() {
+		globalIsDistXL = currentIsDistXL
+	}()
+
 	// need to set this to avoid stale values from other tests.
 	globalMinioPort = "9000"
 	globalMinioHost = ""