SOLR-6554: Speed up overseer operations

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/trunk@1642437 13f79535-47bb-0310-9956-ffa450edef68
SOLR-6554: Removed one-liner methods and unused methods from overseer

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/trunk@1642443 13f79535-47bb-0310-9956-ffa450edef68
LUCENE-6081: Bump language level in IntelliJ configuration for trunk.

This closes #111.

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/trunk@1642446 13f79535-47bb-0310-9956-ffa450edef68