Reduce gRPC dependency footprint, get rid of duplicate classes

[mziccard]

This reduced gRPC dependencies that we include (in particular in the core module) fixes #1278 for good.

@anthmgoogle @garrettjonesgoogle any chance you can have a look? This can also be done at GAX layer to fix googleapis/gax-java#133. Also, is there a reason why proto artifacts (as grpc-google-iam-v1 or grpc-google-pubsub-v1) depend on the whole grpc-all package? I believe that the dependency list there can be heavily reduced.

[coveralls]

Coverage remained the same at 83.896% when pulling d9d23ba on mziccard:reduce-grpc-dependency-footprint into a963ef4 on GoogleCloudPlatform:master.

[garrettjonesgoogle]

Maybe I should bump the priority of the dependency change in gax so that you don't have to make this mess.

[mziccard]

Actually GAX is not a big issue. We use GAX in our google-cloud-core module, but even with the GAX issue fixed I would still want to exclude some of its gRPC dependency (namely all but grpc-protobuf) ingoogle-cloud-core (to reduce its footprint for those modules that depende on it but don't use gRPC). Then in gRPC-based modules I would still have to re-add all grpc dependencies that I previously excluded.

What is causing this mess is the fact that all proto artifacts depend on grpc-all which is as surprising as unnecessary.

[garrettjonesgoogle]

Ahh, the proto artifacts - how much would it help for me to update their dependencies too?

[mziccard]

Ahh, the proto artifacts - how much would it help for me to update their dependencies too?

My guess is that they only need grpc-protubuf, if this is really the case I can get rid of all <exclude> elements for them (there's one for each pom.xml in this PR and 2 in the core module's pom.xml).

It's not a problem to send out this PR and then remove the <excludes>. Releasing releasing new proto artifacts for all services might take you some time.

[coveralls]

Coverage remained the same at 83.896% when pulling 6be9e2c on mziccard:reduce-grpc-dependency-footprint into a963ef4 on GoogleCloudPlatform:master.

[garrettjonesgoogle]

LGTM

[mziccard]

@garrettjonesgoogle thanks for reviewing!