Test credentials are passed with channel arg. Renamed macros and refactored code as per suggestions. Renamed test to proxy_auth and changed it to use simple_request instead of a payload.

Adding connect auth feature. Proxy-Authorization header is being inserted when user creds are present in uri

This reverts commit 3d04e025.

Created test driver to run matrix test against different docker images in GCR and generate a Junit like test result file.