Add Python3.6 to build artifacts

Improve Node and libuv testing and test coverage

Allow Node tests to run with or without UV, change default version to 7, add some portability tests. Also make some more core tests work with libuv

Use unique namespace for each python protoc test

Using the same namespace results in errors when using the c-extension
version of protobuf due to name collisions

C# Readme improvements

ruby mac build environment updates

add ruby example that doesn't use protobuf

Disable libuv core changes in Node library and bump version number

User-Agent "Python-gRPC-" → "grpc-python/".

This brings gRPC Python into conformance with the recommendation in
https://github.com/grpc/grpc/blob/master/doc/PROTOCOL-HTTP2.md.

Backport #9479: Automatedly advance ObjC version numbers

Pin yapf  for v1.1.x

ruby bundle install work around to build packages on mac

Node: fix handling/propagation of server-side serialization errors