python pyspark code autocomplete

[Lonica <fa...@163.com>]

I have test https://github.com/apache/zeppelin/pull/1465 <https://github.com/apache/zeppelin/pull/1465>,
when I build the package after git apply this patch, The problem is still happend
The error stacktrace in %pyspark is:
java.lang.NullPointerException
	at org.apache.zeppelin.spark.PySparkInterpreter.completion(PySparkInterpreter.java:453)
	at org.apache.zeppelin.interpreter.LazyOpenInterpreter.completion(LazyOpenInterpreter.java:122)
	at org.apache.zeppelin.interpreter.remote.RemoteInterpreterServer.completion(RemoteInterpreterServer.java:469)
	at org.apache.zeppelin.interpreter.thrift.RemoteInterpreterService$Processor$completion.getResult(RemoteInterpreterService.java:1742)
	at org.apache.zeppelin.interpreter.thrift.RemoteInterpreterService$Processor$completion.getResult(RemoteInterpreterService.java:1727)
	at org.apache.thrift.ProcessFunction.process(ProcessFunction.java:39)
	at org.apache.thrift.TBaseProcessor.process(TBaseProcessor.java:39)
	at org.apache.thrift.server.TThreadPoolServer$WorkerProcess.run(TThreadPoolServer.java:285)
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
	at java.lang.Thread.run(Thread.java:745)

and the error in %python is:
ERROR [2016-09-28 23:29:20,019] ({qtp659748578-107} NotebookServer.java[onMessage]:261) - Can't handle message
org.apache.zeppelin.interpreter.InterpreterException: org.apache.thrift.transport.TTransportException
	at org.apache.zeppelin.interpreter.remote.RemoteInterpreter.completion(RemoteInterpreter.java:453)
	at org.apache.zeppelin.interpreter.LazyOpenInterpreter.completion(LazyOpenInterpreter.java:122)
	at org.apache.zeppelin.notebook.Paragraph.completion(Paragraph.java:242)
	at org.apache.zeppelin.notebook.Note.completion(Note.java:520)
	at org.apache.zeppelin.socket.NotebookServer.completion(NotebookServer.java:797)
	at org.apache.zeppelin.socket.NotebookServer.onMessage(NotebookServer.java:217)
	at org.apache.zeppelin.socket.NotebookSocket.onWebSocketText(NotebookSocket.java:56)
	at org.eclipse.jetty.websocket.common.events.JettyListenerEventDriver.onTextMessage(JettyListenerEventDriver.java:128)
	at org.eclipse.jetty.websocket.common.message.SimpleTextMessage.messageComplete(SimpleTextMessage.java:69)
	at org.eclipse.jetty.websocket.common.events.AbstractEventDriver.appendMessage(AbstractEventDriver.java:65)
	at org.eclipse.jetty.websocket.common.events.JettyListenerEventDriver.onTextFrame(JettyListenerEventDriver.java:122)
	at org.eclipse.jetty.websocket.common.events.AbstractEventDriver.incomingFrame(AbstractEventDriver.java:161)
	at org.eclipse.jetty.websocket.common.WebSocketSession.incomingFrame(WebSocketSession.java:309)
	at org.eclipse.jetty.websocket.common.extensions.ExtensionStack.incomingFrame(ExtensionStack.java:214)
	at org.eclipse.jetty.websocket.common.Parser.notifyFrame(Parser.java:220)
	at org.eclipse.jetty.websocket.common.Parser.parse(Parser.java:258)
	at org.eclipse.jetty.websocket.common.io.AbstractWebSocketConnection.readParse(AbstractWebSocketConnection.java:632)
	at org.eclipse.jetty.websocket.common.io.AbstractWebSocketConnection.onFillable(AbstractWebSocketConnection.java:480)
	at org.eclipse.jetty.io.AbstractConnection$2.run(AbstractConnection.java:544)
	at org.eclipse.jetty.util.thread.QueuedThreadPool.runJob(QueuedThreadPool.java:635)
	at org.eclipse.jetty.util.thread.QueuedThreadPool$3.run(QueuedThreadPool.java:555)
	at java.lang.Thread.run(Thread.java:745)
Caused by: org.apache.thrift.transport.TTransportException
	at org.apache.thrift.transport.TIOStreamTransport.read(TIOStreamTransport.java:132)
	at org.apache.thrift.transport.TTransport.readAll(TTransport.java:86)
	at org.apache.thrift.protocol.TBinaryProtocol.readAll(TBinaryProtocol.java:429)
	at org.apache.thrift.protocol.TBinaryProtocol.readI32(TBinaryProtocol.java:318)
	at org.apache.thrift.protocol.TBinaryProtocol.readMessageBegin(TBinaryProtocol.java:219)
	at org.apache.thrift.TServiceClient.receiveBase(TServiceClient.java:69)
	at org.apache.zeppelin.interpreter.thrift.RemoteInterpreterService$Client.recv_completion(RemoteInterpreterService.java:358)
	at org.apache.zeppelin.interpreter.thrift.RemoteInterpreterService$Client.completion(RemoteInterpreterService.java:342)
	at org.apache.zeppelin.interpreter.remote.RemoteInterpreter.completion(RemoteInterpreter.java:449)
	... 21 more