Support PUBSUB_EMULATOR_HOST environment variable

[blowmage]

gcloud-ruby should support the PUBSUB_HOST PUBSUB_EMULATOR_HOST environment variable and connect to service specified in it. This will enable connecting to an emulator running locally, similar to how the Datastore emulator works.

See GoogleCloudPlatform/gcloud-common#48

[quartzmo]

I believe the correct variable should be PUBSUB_EMULATOR_HOST, per the official docs' Setting environment variables. gcloud-node also now uses PUBSUB_EMULATOR_HOST.

[quartzmo]

See googleapis/google-cloud-node#1125 for the complete gcloud-node change for this variable name.

[quartzmo]

@dlorenc Be aware that in our next release, the gcloud-ruby Pub/Sub client will be using gRPC instead of Rest.

@hbchai commented that the Pub/Sub emulator also supports gRPC. (I haven't tested it yet.)

[dlorenc]

Thanks for the update!

[quartzmo]

Just an implementation note: Following the lead of gcloud-node, the gRPC connection to the emulator should be insecure (no credentials), as in this example:

stub = Helloworld::Greeter::Stub.new('localhost:50051', :this_channel_is_insecure)

[dlorenc]

Any updates here?

[quartzmo]

@dlorenc We are still working on #314.

@blowmage Do you think we can add this issue to the Datastore v1beta3/GRPC milestone? Do you have any time now to work on it?

[blowmage]

If we get this implemented then we may want to put it in a point release before Dataset/GRPC, since we don't know when that will be ready to be released.