Don't use environment variables for command line options

Jakefile and Gulpfile use process.env to store command line options. These can become confused when a real environment variable is defined that happens to share a name with one of our options.

[weswigham]

This was a feature that, AFAIK, people actually used. I'd poll the rest of the team to see if they actually use it or not. Also, it can't be removed from Jake, its part of its builtin argument parsing infrastructure. It can be removed from gulp, however, as it was only added to mimic Jake's functionality.

Since we don't have a port option any more (#9985), this is no longer an issue for me. Closing.