SOLR-6233: Minor refactorings provided by Steve Davids.

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/branches/branch_5x@1626824 13f79535-47bb-0310-9956-ffa450edef68
SOLR-6481: CLUSTERSTATUS action should consult /live_nodes when reporting the state of a replica

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/branches/branch_5x@1626828 13f79535-47bb-0310-9956-ffa450edef68
SOLR-6484: SolrCLI's healthcheck action needs to check live nodes as part of reporting the status of a replica

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/branches/branch_5x@1626829 13f79535-47bb-0310-9956-ffa450edef68
LUCENE-5969: let AssertingCodec implement RandomAccessOrds, and test it directly too

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/branches/branch_5x@1626830 13f79535-47bb-0310-9956-ffa450edef68