fix(units): Relax ordering requirements for now.

The current cloudinit implementation blocks when starting units which
causes it to deadlock the boot process if a system cloud config starts a
user cloud config because the user configs want to run after system is
done. Until cloudinit switches to non-blocking calls user configs will
go back to just depending on coreos-setup-environment.service.
Merge pull request #76 from marineam/units2

fix(units): Relax ordering requirements for now.