Show LuceneTestCase LiveIndexWriterConfig changes with deltas

With tests.verbose, each time the IWC is changed the whole thing is printed out. But this is overly verbose during indexing and does not show you what changed, so you have to stare hard at tons of IWC.toString()s and figure it out.

Instead I think we should just show a diff?

   [junit4]   1> NOTE: LuceneTestCase: randomly changed IWC's live settings:
   [junit4]   1> - ramBufferSizeMB=16.0
   [junit4]   1> + ramBufferSizeMB=3.0
   [junit4]   1> - maxBufferedDocs=308
   [junit4]   1> + maxBufferedDocs=-1