Enable gRPC for datastore API.

[dhermes]

NOTE: Has #2097 as diffbase.

[dhermes]

@tseaver I don't have a flag for disabling it, but am happy to add it, just wanted to here from you about it.

[tseaver]

The environment flags for pubsub and logging were basically there to allow me to test with the gRPC team, without turning the feature on by default. We can probably leave them out here, if you don't feel paranoid about the gRPC stuff breaking us.

[dhermes]

if you don't feel paranoid about the gRPC stuff breaking us

I don't feel paranoid

[tseaver]

I don't feel paranoid

Hmm.

[dhermes]

Hmm aside, let's get #2097 settled and then move back here. (I'll resolve the merge conflict.)

[dhermes]

@tseaver Rebased after #2097, PTAL.

The question remaining is how to update make_operations_grpc.py to have all the imports. Should I just import all the names from gcloud.datastore._generated.datastore_pb2?

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As for worry about gRPC, I was more saying I'm not worried about people having imports work but wanting to turn it off. And those people can just hack and edit the module-private _HAS_GRPC

[tseaver]

The question remaining is how to update make_operations_grpc.py to have all the imports. Should I just import all the names from gcloud.datastore._generated.datastore_pb2?

This is the canonical case for from foo import *, even.

[dhermes]

Trying to avoid the import *

[dhermes]

@tseaver Check out the latest commit

[tseaver]

LGTM