Add infra role which just has consul

Having the build node resonsible for slurping upstream mirrors,
building native packages, and creating a repo creates an awkward situation
where these things must all happen before it can consume its own repo
to install the packages it has built. Therefore the build role has
been split into both build, which will simply build the repo and serve
it via http, and infra, which will be responsible for infrastructure
services beginning with consul but spreading to monitoring and log
aggregation as those features are added.