Continuous replicator does not back off retries

A continuous replicator that reaches the stopped state, for a reason that the core replicator believes to be network dependent and transient, will attempt to start a new replicator.  It should be doing exponential backoff.  It is not doing so, because it sets the retry count to 0 as soon as each new replicator reaches the connecting state.

https://github.com/couchbase/couchbase-lite-android-ce/issues/11