[UIMA-3759] Using profiler, determined that the test driver is holding on to instances of the test classes.  If those classes, in turn, have instance variables holding onto large objects, and no tearDown() sets these to null, this causes an accum. of memory use. It looks like on some JVMs/OSs, we were near the max heap.  Added tearDown cleanups to the major heap users. 

git-svn-id: https://svn.apache.org/repos/asf/uima/uimaj/trunk@1588506 13f79535-47bb-0310-9956-ffa450edef68