fix(agent): Only call daemon-reload if necessary

Calling daemon-reload in systemd can cause open sytemd jobs to
stall. We can minimize the impact this has on fleet my limiting
our usage of daemon-reload.
fix(agent): Simplify purging jobs

The Agent.StopJob function is intended to be triggered by users and has
a very destructive impact on the cluster. When calling Agent.Purge, the
churn created by StopJob causes jobs that need to be rescheduled to
completely stop. Manually purging state and ignoring peers allows jobs
to reliably get rescheduled.
test(functional): Ensure ConditionMachineOf carries through reboots
refactor(agent): Remove unnecessary call to VerifyJob in Purge