Pubsub API should provide a way to synchronize a set of operations

[gcbirzan]

The pubsub API provides no easy way to make sure a bunch of publishes finish before continuing. You have to either deal with batches yourself or wait on every Future returned. A context manager would do the job, or even a wait method on the client.

[theacodes]

@lukesneeringer what do you think?

[lukesneeringer]

Seems reasonable to me. asyncio does have a mechanism to wait on multiple futures but that does not help anyone on earlier versions of Python.

[sduskis]

@theacodes, do you think this is still a GA blocking issue?