Rewrite installer to find processes using systemctl

[ozdanborne]

The installer uses python's psutil and regex statements to track down the processes it plans to restart later. It then uses systemctl restart to restart the task.

We should switch to use systemctl status to track down processes instead, since we are already dependent on systemctl restart. This would mean we support all platforms using systemd.

It's recently been reported that our installer doesn't work using dcos-gce with centos .

[ozdanborne]

Fixed by #38 !