Remove underlying stream from the WALWriter.
Tests reading and writing data using writers now use Minicluster.

Conflicts:
	streaming/pom.xml
	streaming/src/main/scala/org/apache/spark/streaming/util/WriteAheadLogWriter.scala
	streaming/src/test/scala/org/apache/spark/streaming/util/WriteAheadLogSuite.scala
Remove unused method
Fix broken test. Call getFileSystem only from synchronized method.
Restore old build directory after tests
Merge pull request #17 from harishreedharan/driver-ha-wal

Use Minicluster for WAL tests.