Blocker Description
After some investigation, the root cause seems to be that `kill_job` expects the executor to launch a task with `CreateProcess` and the put that into a job object, but in `MesosContainerizerLaunch::execute`, we're actually just calling `execvpe`. We should refactor this code so that this gets properly contained inside a job object on Windows.
Additionally, since we're not propagating errors when an attempt to kill a process group fails, we get very mysterious errors and hanging tests (see review at [1]), so we should fix that too.