DERBY-6238: Lock timeout in GrantRevokeTest.testGrantRollbackAndCommit

Improve error reporting to help debugging:

- Check that all exceptions are as expected
- Provide stack trace for all unexpected exceptions
- Dump lock table on lock timeouts

git-svn-id: https://svn.apache.org/repos/asf/db/derby/code/trunk@1488896 13f79535-47bb-0310-9956-ffa450edef68