ostbuild: Tighten build process significantly

ostbuild: Tighten build process significantly

First, "resolve" now just picks git commits.  We don't expand
config-opts and patches, nor do we generate tree contents.  This makes
the generated files *much* more human editable.

Next, fold "build-components" and "compose" into just "build".  One
never really wants to just build components.  This lets us eliminate
binary snapshots as a concept; instead we always have a combination of
source snapshot and component/ refs.