Jenkins access issues for `vagrant` machines

The `infra-vagrant` machines have been using an explicit user list to determine who can use them. This should not be the case and the default access for all people in the committers/triage teams should be able to run on those systems (Or possible restricted to the infrastructure* teams)

It's unclear why this was originally done, but I have so far failed to be able to switch it to work any other way. This issue will cover trying to resolve that.

Start by tracing how Jenkins access for the `infra-vagrant` machines is currently determined, beginning with the explicit user list mentioned in the issue. Compare the desired committers/triage or infrastructure-team access with the current behavior. Done means the machines no longer depend on an explicit user list and the intended teams can run on them.

Written by the indexing model from the issue text.