SOLR-6843: JMX RMI connector should be disabled by default but can be activated by setting ENABLE_REMOTE_JMX_OPTS to true in solr.in.(sh|cmd).

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/branches/branch_5x@1644979 13f79535-47bb-0310-9956-ffa450edef68