fix(coreos-base/oem-gce): Replace curl's --retry with block_until_url

Curl will not retry after most errors, just connection timeouts and some
HTTP errors. In our case the most likely error is network unreachable.
Instead use our simple-minded but trusty block_until_url script to wait.
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
Merge pull request #544 from marineam/block

fix(coreos-base/oem-gce): block_until_url and coreos-setup-environment
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-*): 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.