feat: Allow exclude option to be configured from command line

Allow exclude option to be passed in from command line.

Example:
```sh
$ karma start --exclude=lib/foo.js,lib/bar.js
```

Use case:  I have two different versions of a library that I want to test against.  Instead of having two karma files, I just include both versions of the library in the karma.conf.js and exclude one or the other through a Makefile when testing.