[HOTFIX][Streaming] Handle port collisions in flume polling test

This is failing my tests in #1777. @tdas

Author: Andrew Or <andrewor14@gmail.com>

Closes #1803 from andrewor14/fix-flaky-streaming-test and squashes the following commits:

ea11a03 [Andrew Or] Catch all exceptions caused by BindExceptions
54a0ca0 [Andrew Or] Merge branch 'master' of github.com:apache/spark into fix-flaky-streaming-test
664095c [Andrew Or] Tone down bind exception message
af3ddc9 [Andrew Or] Handle port collisions in flume polling test
SPARK-2882: Spark build now checks local maven cache for dependencies

Fixes [SPARK-2882](https://issues.apache.org/jira/browse/SPARK-2882)

Author: Gregory Owen <greowen@gmail.com>

Closes #1818 from GregOwen/spark-2882 and squashes the following commits:

294446d [Gregory Owen] SPARK-2882: Spark build now checks local maven cache for dependencies