set_group: don't copy update.gz, but do copy the dev container

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.
build_image: when generating update payload don't generate metadata

This feature was removed from delta_generator.
Merge pull request #286 from marineam/version2

minor build fixes