[FLINK-1038] remove false registry closing
[FLINK-1038] some amendments to the RemoteOutputCollectorFormat
* rethrowing exceptions
* toString() for RemoteOutputCollectorFormat (visible in web frontend)
* unique RMI IDs for different data sinks
Merge remote-tracking branch 'origin/FLINK-1038' into FLINK-1038

Conflicts:
	flink-java/src/main/java/org/apache/flink/api/java/io/RemoteCollectorImpl.java
	flink-java/src/main/java/org/apache/flink/api/java/io/RemoteCollectorOutputFormat.java
Merge branch 'FLINK-1038' into private-master