LUCENE-5339: migrate some more tests; fix 'ignores IntsRef.offset bug' in TaxoFacetCounts; add FacetTestCase.getFacetCounts

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/branches/lucene5339@1543506 13f79535-47bb-0310-9956-ffa450edef68