[SPARK-5788] [PySpark] capture the exception in python write thread

The exception in Python writer thread will shutdown executor.

Author: Davies Liu <davies@databricks.com>

Closes #4577 from davies/exception and squashes the following commits:

eb0ceff [Davies Liu] Update PythonRDD.scala
139b0db [Davies Liu] capture the exception in python write thread

core/src/main/scala/org/apache/spark/api/python/PythonRDD.scala

@@ -248,13 +248,13 @@ private[spark] class PythonRDD(
       } catch {
         case e: Exception if context.isCompleted || context.isInterrupted =>
           logDebug("Exception thrown after task completion (likely due to cleanup)", e)
-          worker.shutdownOutput()
+          Utils.tryLog(worker.shutdownOutput())
 
         case e: Exception =>
           // We must avoid throwing exceptions here, because the thread uncaught exception handler
           // will kill the whole executor (see org.apache.spark.executor.Executor).
           _exception = e
-          worker.shutdownOutput()
+          Utils.tryLog(worker.shutdownOutput())
       } finally {
         // Release memory used by this thread for shuffles
         env.shuffleMemoryManager.releaseMemoryForThisThread()