SOLR-4629: TestReplicationHandler improvements (merge r1467723)
 - new testEmptyCommits
 - numFound assertion refactoring
 - reduce excessive test sleeping in rQuery
 - new "wait" option to make fetchindex block
 - refactor core reload test to wait for the startAt time to change





git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/branches/branch_4x@1467725 13f79535-47bb-0310-9956-ffa450edef68