add ability to set delay on mock response
testReplicationOnlineExtraneousChangeTrackers() passes

https://github.com/couchbase/couchbase-lite-android/issues/398
testGoOfflinePusher() passes

https://github.com/couchbase/couchbase-lite-android/issues/398
testOnlineOfflinePusher() passes

https://github.com/couchbase/couchbase-lite-android/issues/398