lakitu: google-osconfig-agent: add a pre-work service

The Systemd service "google-osconfig-init" does the pre-work for

TEST=Presubmit and also verified that OSConfig runs user scripts after
     restarting the VM.
RELEASE_NOTE=Script based guest-policies are now applied on each boot
             instead of only on the first boot of the instance

Change-Id: I62fffd542f7eea2bc29fe5c0817a0bba1e90c900
3 files changed