LUCENE-5896: Use local random instance rather than global in LuceneTestCase

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/branches/branch_4x@1619213 13f79535-47bb-0310-9956-ffa450edef68
SOLR-6393: TransactionLog replay performance on HDFS is very poor.

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/branches/branch_4x@1619218 13f79535-47bb-0310-9956-ffa450edef68