Create tagging job for the puppet-agent

Create a Jenkins job to automate Steps (4) and (5) in e.g. PA-1659. This will come after the components are tagged and the required resources (both project-level and component-level) are calculated, but before actual work is done (packages are built and shipped, integration tests are run, etc.). The job should:

1. Build the puppet-agent package on one platform (el-7-x86_64)
2. If the build succeeds, tag the puppet-agent project with whatever the release version is
3. Re-archive the puppet-agent project, checked out at the tagged release. Note that this version of the project should be what will be passed along in future steps of the package-validation pipeline.

Note that before building the puppet-agent project, the job should first check if the agent is already tagged at that release. If it is, then it can pass through. This way, we avoid rebuilding the project in the agent tagging step in case the package validation pipeline needs to be re-kicked.

The "actual work" part should use the TAR ball generated from the agent tagging job.