created separate class for Http2Server.

images.

Add response parameters to custom_metadata streaming request for Node and PHP
clients.

The Java server does not respond with separate initial and trailing
metadata when there is no response data - it is only emiting the
requested trailing metadata. Adding the response parameters to the test
(in accordance with the specification) avoids this, but I will open a
separate issue to investigate the Java behavior.

Some of these files contain the magic string "DO NOT EDIT" but we do
not wish for our tests to depend upon that.

This should address the difference in how we ask users to install
grpcio-tools and the files the user ends up downloading from PyPI.