I don't think this is just for metabuildbot - this will be useful for anyone doing development on a system without a browser.  Would `phantom` (and below, `phantomtest`) be a better name?

Also, it's not clear what I should install to get this to work.  I guessed `npm install phantomjs`, after which I get
```
Running "karma:ci" (karma) task
INFO [karma]: Karma server started at http://localhost:9876/
INFO [launcher]: Starting browser PhantomJS
WARN [watcher]: Pattern "/home/dustin/code/buildbot/t/buildbot/www/buildbot_www_test/scripts/filters/*.js" does not match any file.
INFO [PhantomJS 1.9 (Linux)]: Connected on socket id cuIvVjeRKfdSU1ivXTed
PhantomJS 1.9 (Linux): Executed 1 of 1 SUCCESS (0.144 secs / 0.011 secs)
ERROR [launcher]: Cannot start PhantomJS

Done, without errors.
```
which sends some mixed messages!