Rework testBatcherBatchSize5 to be more robust

https://github.com/couchbase/couchbase-lite-java-core/issues/287
Fix attempt for Jenkins test failure testRetryQueueDeadlock()

- Upgrade MockWebserver to later version, since there was a stacktrace coming from that package (and I'm not sure why such an old version was being used)
- Tweak delays so this test runs faster

https://github.com/couchbase/couchbase-lite-java-core/issues/287#issuecomment-57241711