nailgun 0.9.1 (zombie formula)

As per #21880 nailgun was removed because it was woefully outdated and had moved to a new packaging format. This commit brings the nailgun formula back from the boneyard and updates it to 0.9.1.

I've also taken a stab at writing a test, but there's a few ways that it's not ideal. Just testing the ng command would miss testing the server, but there's no good way that I can see to spin up the ng-server without backgrounding the process and waiting for it to bind to its port.

Also, if there's a way to get an unassigned port from the ephemeral range in Ruby, I'd rather do that than hard code 8765, but I didn't find a simple way to pick an unused port. 
Remind me: did you submit this upstream? If so, can you link as a comment in the `nailgun.rb` file where it was submitted? Thanks.