Investigate and possilby mitigate thread safty issue in CalciteSolrDriver.java

Detected by sonatype-lift in https://github.com/apache/solr/pull/397

Tagging streaming expressions since SolrClientCache's javadoc indicates that it is (at least originally) for reuse of clients by tuple streams

It seems like problems may arise if tests start more than one core container per jvm/classloader