fix(coreos-base/oem-gce): Silence bogus /etc/hosts error

On first boot /etc/hosts doesn't exist yet, causing an error to be
logged. This is a bit misleading
fix(coreos-base/oem-gce): Robustify the GCE user-data script.

 - Provide some logging on what actually happened.
 - Tolerate empty user-data, just no-op.
 - Apply both project and instance data.
Merge pull request #542 from marineam/gcefix

GCE fixes
churn(coreos-base/coreos-cloudinit): Move units into cloudinit repo.
fix(etcd+fleet): Add dependency on user-config.target

Since etcd and fleet are often configured by cloud configs they should
never start before the assorted calls to coreos-cloudinit finish.
bump(coreos-base/coreos-init): Deprecate old addon units.
fix(coreos-base/oem-gce): Rename gce-setup-environment

The setup-environment script should be named coreos-setup-environment so
that it is called by the standard coreos-setup-environment.service
fix(coreos-base/oem-*): Use new targets for metadata services

User configs should be handled after system-config.target but before
user-config.target.
fix(coreos-base/oem-rackspace): Rely on generic configdrive units.

Config drive is now supported on all VM platforms so it doesn't need to
be in the rackspace OEM any more.
fix(coreos-base/oem-vagrant): Use generic cloud config unit.