Renovates gRPC instrumentation in preparation of standard parsing

[codefromthecrypt]

This fixes some glitches in preparation of #999

• Bumps gRPC to 1.29 (there was no impact)
• GrpcClientRequest and GrpcServerRequest unwrapped this, not the call.
• Anonymous GrpcClientParser and GrpcServerParser used ErrorParser unnecessarily
  • This is implicitly done in the Zipkin span handler
• Status.cause was ignored
  • This led to a less precise "error" tag
• Client headers were unnecessarily null during sampling. This was caused by
  too eager allocation of a span.
• ClientCall.Listener was wrapped twice
• Most ClientCall hooks were not placed in scope
• ServerCall's span was started too late

[codefromthecrypt]

FYI continuous-integration/travis-ci/pr rarely passes when you change things in the pom. ex it fails in invoker tests due to drift between master and whatever is in the PR. I'm not sure what this is about, but seems to explain why we get winky (one red one green) builds on changes sometimes.

[anuraaga]

Left some comments about how we handle error spans. Since grpc-java stubs implement the lifecycle, which includes propagating errors into close, I believe we don't have to do as much work as we're doing.

[codefromthecrypt]

Thanks for the thoughtful consideration @anuraaga. This is much better than before

[codefromthecrypt]

force pushed as I have no other good ideas on how to get the mockito change to pass in travis.

[codefromthecrypt]

I'm going to special case the mockito depedendency as I cannot get travis to pass in invoker mode in any way

[codefromthecrypt]

force pushed again, with specific includes on the grpc invoker tests. At least locally, this doesn't use mockito at all now.

[codefromthecrypt]

I am removing the mockito flag @anuraaga. It is unsupportable and there are so many other things worth time than flailing on this

Mockito cannot mock this class: class io.grpc.MethodDescriptor.

Can not mock final classes with the following settings :

 - explicit serialization (e.g. withSettings().serializable())

 - extra interfaces (e.g. withSettings().extraInterfaces(...))

You are seeing this disclaimer because Mockito is configured to create inlined mocks.

You can learn about inline mocks and their limitations under item #39 of the Mockito class javadoc.

Underlying exception : org.mockito.exceptions.base.MockitoException: Could not modify all classes [class io.grpc.MethodDescriptor, class java.lang.Object]

[codefromthecrypt]

fingers crossed.