LUCENE-5595: try to improve test efficiency

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/branches/branch_5x@1643805 13f79535-47bb-0310-9956-ffa450edef68
SOLR-6829: Added getter/setter for lastException in DIH's ContextImpl

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/branches/branch_5x@1643860 13f79535-47bb-0310-9956-ffa450edef68
SOLR-6778: Add more details about getting started in solr/README.txt

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/branches/branch_5x@1643861 13f79535-47bb-0310-9956-ffa450edef68
LUCENE-6097: make abort/waitForMerges private

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/branches/branch_5x@1643895 13f79535-47bb-0310-9956-ffa450edef68
LUCENE-6099: add FilterDirectory.unwrap and FilterDirectoryReader.unwrap

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/branches/branch_5x@1643903 13f79535-47bb-0310-9956-ffa450edef68
fix broken failonerror=false in these targets

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/branches/branch_5x@1643941 13f79535-47bb-0310-9956-ffa450edef68