grpc python http_proxy is sensitive to case and schema is not optional

[swuecho]

✗ http_proxy=localhost:12345 python greeter_client.py
E0619 00:36:52.389945000 4728600000 http_proxy.cc:62] 'localhost' scheme not supported in proxy URI
Greeter client received: Hello, you!
✗ HTTP_PROXY=localhost:12345 python greeter_client.py
Greeter client received: Hello, you!
✗ HTTP_PROXY=http://localhost:12345 python greeter_client.py
Greeter client received: Hello, you!

✗ http_proxy=http://localhost:12345 python greeter_client.py
Greeter client received: Hello, you!

for test: use https://github.com/swuecho/hello_grpc, but change the port in server to 50051.

[swuecho]

not an issue of grpc-tools. should be grpc client implementation problem.