ref(logger): remove /app/bin/boot script

The use case for /app/bin/boot was to handle a bunch of tasks that
are better handled with systemd. Removing the reliance on bin/boot
follows The Docker Way.
I didn't think about that use case. Is there a good way to run a while loop forever in a `ExecStartPost`? I tried with

    /bin/sh -c "while true; do etcdctl set /deis/logs/port 514 --ttl 10; sleep 5; done"

but that showed up in fleet as `Post-Exec`.