SOLR-6747: Add an optional caching option as a workaround for SOLR-6586.

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/trunk@1640582 13f79535-47bb-0310-9956-ffa450edef68
SOLR-6365 "implicit  requesthandler (specifiedin code) takes lower precedence over <initParams>"

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/trunk@1640594 13f79535-47bb-0310-9956-ffa450edef68