This splits the platform creation into 3 parts:
* base - create the initial directory based on the parent platform
* prepare - run prepare commands and apply all changes
* cleanup - apply cleanups and cleanup commands
This has cacheing advantages in that prepare_commands and cleanup changes
only cause the minimal amount of rebuilds.
Additionally, it ensures that the mtimes are zeroed out (from the
previous checkout) both when the prepare and cleanup commands are run.
This is actually important, since these often generate caches (for
example fontconfig ones) which rely on zeroed mtimes so they match
what will be deployed.
Closes: #277
Approved by: alexlarsson
All this does is construct a finish arg, but it makes it a lot nicer
to create extra-data using manifest. Additionally, it allows you to
create per-arch extra data if you set only-arches on the source.
Closes: #40
Approved by: alexlarsson
Alexander Larsson