Clean up how test env variables are parsed

Oslo and cookiecutter and other projects were using
variable to parse test environment vaiables. Let us
do this in hacking

This is copied from 739627bf79619f8 Use cleaner version from
cookiecutter OpenStack template

Change-Id: Ibdaa0a63acf6c5590d10a637502e710caad3965d
Merge "Clean up how test env variables are parsed"