Gerrit Integration Support

[rmustacc]

We have a number of things that run in gerrit today that cannot take advantage of the glory of buildomat. This ticket is here just for tracking around the ability to integrate into gerrit and watch changes much like we do on github today.

[jclulow]

NB: I am part way through a first version of this, in https://github.com/oxidecomputer/squire