SOLR-4550: Create a stress test for CachingDirectoryFactory

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/branches/lucene_solr_4_2@1458039 13f79535-47bb-0310-9956-ffa450edef68
SOLR-4553: attempt to harden #testNodeWithoutCollectionForwarding

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/branches/lucene_solr_4_2@1458040 13f79535-47bb-0310-9956-ffa450edef68