Fix some issues with the benchmark code

[murgatroid99]

The change in any_grpc.js allows code packaging tools such as pkg to correctly process that require call.

The old grpc library is now an optional dependency, so that installation of other packages can proceed if in environments where that package is not supported, particularly when the runtime is a newer version of Node.

When calling RunServer on a worker with a port of 0, the response now reports the actual bound port instead of 0.

The new worker.js is there for manual testing. It expects two workers to be running at the specified ports on localhost, and it instructs them to run a simple benchmark.