Of note in this version upgrade is the replacement of NrtManager by
ControlledRealTimeReopenThread, which has a different API as used by
SubIndex.
Change-Id: Id34eb8e75bb07a38be9b5ed9a1cdeaf195774b58
SolrCloud can be used instead of Lucene by adding "type = SOLR"
under [index] and "url = <zookeeper-url>" under [index "solr"]
in gerrit.config.
Change-Id: I0ff8579c5e23c58b16f3605bc20eba4e80fb40fc