DERBY-6612 Add code to harness tests to allow running under JDK9 VMs.

Backported cleanly from trunk as "svn merge -c 1602266 <repo>".



git-svn-id: https://svn.apache.org/repos/asf/db/derby/code/branches/10.10@1602299 13f79535-47bb-0310-9956-ffa450edef68