Code review comment for ~andreserl/maas:1.9_lp1732703

First, and foremost, this only applies to *Trusty*.

Trusty uses upstart by default. When you install systemd, /sbin/init will *NOT* point to /lib/systemd/systemd/.

You need to manually modify it to use /sbin/init, hence this patch works.

This has been already tested in multiple environments.