clear the base path if no upstreams, improvements to vagrant config

@tpetr This is to clear the base path from zk in the case where all upstreams for the service have been removed. Should fix some issues around a service getting renamed, but keeping the same base path
you're on the right track, but this will be executed on each load balancer when a `BaragonRequest` is being applied (we have no guarantee that it'll be applied correctly on all agents yet). A better place for this is inside the `commitRequest()` method in `RequestManager`