unit: check replicator listener events (#2458)
unit: check replicator listener events (#2458)

* when conflicts happens, make sure there is only single event is fired.
* validated when exception happens and when resolver succeeds
couchbase/couchbase-lite-ios,couchbase/couchbase-lite-ios,couchbase/couchbase-lite-ios,couchbase/couchbase-lite-ios,couchbase/couchbase-lite-ios,couchbase/couchbase-lite-ios