PubsubIO: create subscription on different project than the topic

If you try to read a public pubsub topic in the DirectRunner, it will fail with 403 when trying to create a subscription. This is because it tries to create a subscription on the shared public data set.

There is an example used in https://github.com/googlecodelabs/cloud-dataflow-nyc-taxi-tycoon and the dataset is projects/pubsub-public-data/topics/taxirides-realtime. I discovered that I could not read this in the DirectRunner even though the codelab works. But that 1.x codelab also does not work in the InProcessPipelineRunner, so it has been broken all along.

So you cannot read public data or any other read-only data using PubsubIO.