Update agent builds to rely solely on location of runtime, not git ref

Currently the agent builds require information on both the git ref and location of agent-runtime to correctly pull settings and packages.

It just happens to be that tags match both ref and location, so we can get away with 'one piece' of information. However, this makes local development and development builds near impossible unless we flood the build server with dev tags.

We should update the agent/runtime/vanagon to do the following:

1. publish the project settings for puppet-runtime as JSON in a text file to the build server, likely under the exact same directory that the packages go under.
2. Update the agent to pull settings from that file, and not check out the entire runtime project from git.
3. Update the agent's puppet-runtime.json to only supply information on package version and the location of the runtime build (i.e. remove any need to supply a git ref)

In this new scenario we should be able to supply whatever location we want to the agent (even a non-tagged location) and still have the agent pull settings/packages correctly