Fixed TestParallelRendering which was hanging.

TestParallelRendering was not originally designed to be run as a
test. Fixed. It does not do image comparison but at least runs as
part of the test suite. This class is covered well in the ParaView
testing suite.

Change-Id: Ic579396983698c5448b806ce6082b37a9cd8d4b5
Merge topic 'fixed-test-parallel-rendering' into master

6daacef0 Fixed TestParallelRendering which was hanging.