flush stream after WebSocket handleMessage

Author: starofys

util/src/main/java/io/kubernetes/client/util/WebSocketStreamHandler.java

@@ -94,6 +94,7 @@ protected void handleMessage(int stream, InputStream inStream) throws IOExceptio
     try {
       OutputStream out = getSocketInputOutputStream(stream);
       ByteStreams.copy(inStream, out);
+      out.flush();
     } finally {
       inStream.close();
     }