Push environment arguments to the client runner

This adds all environment arguments from the CLI into the runner query string.

Example:

`$ node_modules/.bin/intern-runner config=tests/intern_browser fun_stuff=popcorn`

In the configuration:
```
define(['intern/lib/args'], function (args) {

var fun = args.fun_stuff;
```

Any ideas how to test this feature properly? Hopefully without spawning new processes.