LUCENE-5207: Better classloade test: It now uses a completely synthetic class, so its 100% unreachable from main classloader. Also remove the static Opcodes imports

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/branches/lucene5207@1523426 13f79535-47bb-0310-9956-ffa450edef68