feat(app-emulation/google-daemon): initial google daemon

This installs the google_daemon to /usr/share/oem/google_daemon. The
service files are not installed but will instead be installed by the
cloud-config.yml
bump(coreos-base/oem-gce): install the google-compute agent
feat(app-emulation/google-startup-scripts): initial commit
feat(coreos-base/oem-gce): add google-startup-scripts
feat(coreos-base/oem-gce): add the gce-add-metadata-host service

One of the requirements of GCE is setting up the metadata host. Do this.
fix(coreos-base/oem-gce): make gce's cloudinit oneshot