Allowing arguments to be passed to grunt tasks

I couldn't figure out from the current configuration and examples how to pass arguments/options to grunt tasks. My use case is that I'm trying to run multiple e2e test suites simultaneously, which means passing the same grunt task different tags, i.e.

```
grunt test:e2e --tags=@tag1
grunt test:e2e --tags=@tag2
```

This PR builds the options based off an object passed during configuration.