update.gz and .meta will not be generated any more by default.
And previously the dev container was only being uploaded to the default
'beta' release directory so it wasn't available in a useful location.
Copying it to all the release directories should help with that.
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.