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.
add(toolbox): Adding toolbox to coreos-base
feat(coreos-base/oem-ami): Adding support for openstack and brightbox

Added USE flags for specifying the provider (ec2, openstack, or brightbox). Renamed to oem-ec2-compat.
Merge pull request #541 from crawford/oems

feat(coreos-base/oem-ami): Adding support for openstack and brightbox
Merge pull request #543 from crawford/toolbox

add(toolbox): Adding toolbox to coreos-base
Merge pull request #542 from marineam/gcefix

GCE fixes
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
bump(sys-apps/portage): sync with upstream

portage-2.2.8-r1 is stable.
feat(sys-apps/portage): Adding repos.conf patch to ebuild

Pulling in the patch mentioned here
(https://bugs.gentoo.org/show_bug.cgi?id=507284). This adds support for the
'disabled' attribute in repository sections within repos.conf.