Use pubsub fake written by the pubsub team instead of LocalPublisherImpl

[garrettjonesgoogle]

It isn't available in open source quite yet.

[aozarov]

We could use this in the meantime: https://pantheon.corp.google.com/storage/browser/pubsub/tools/

[garrettjonesgoogle]

here is the LocalPublisherImpl class: https://github.com/GoogleCloudPlatform/gcloud-java/blob/pubsub-alpha/gcloud-java-pubsub/src/main/java/com/google/gcloud/pubsub/spi/testing/LocalPublisherImpl.java