maint(generate_au_zip): Drop old update service uploader
fix(core_roller_upload): Use new payload names and upload path.

As of 4e85b172 the build system generates the update payload using the
coreos_production_update prefix, so use that instead. Use the release
version in the storage path instead of a disk image MD5; the version is
sufficiently unique and the no need for the obfuscation.

Drop the disk image copy in the download storage that I tacked in, that
will go into a new core_promote script that I have written but not
tested yet (need an alpha release to promote!!).
feat(set_lsb_release): Write configured group to /etc instead of /usr

The /usr images must be identical across groups so that information is
static. Eventually the default will be 'stable'
Merge pull request #243 from marineam/groups

More release/build script updates for beta prep
Merge pull request #242 from marineam/c10n

maint(generate_au_zip): Drop old update service uploader
fix(set_lsb_release): Set default GROUP= from arg again.

This makes sure developer builds stick to the developer group. After
commit c3d07e94 developer PXE/ISO images would report as 'alpha'.
Merge pull request #244 from marineam/dev-group

fix(set_lsb_release): Set default GROUP= from arg again.
add(image_set_group): New script to set the update group in prod images.

For generating images for groups other than the one given to build_image
run this script along with the usual image_to_vm.sh commands. To avoid
ambiguity with the 'latest' symlink, this script creates $group-latest
symlinks instead. build_image creates the new symlink too.
Merge pull request #245 from marineam/set-group

add(image_set_group): New script to set the update group in prod images.
add(core_promote): A script for bumping a channel to a new version.