DERBY-6650: Lucene tests fail on compact profile 2

Implement IndexOutput.getChecksum() which is required by Lucene 4.8.
Lucene 4.8 works on compact profile 2.

git-svn-id: https://svn.apache.org/repos/asf/db/derby/code/trunk@1609428 13f79535-47bb-0310-9956-ffa450edef68