It is now possible to define a partition layout via `mpp-define-image`.
The defined layout is actually written to a temporary sparse file and
read back via `sfdisk`, so that all partition data like `size` and
`start` include actual padding and such. The `image` variable will be
defined with `size` and `layout` keys, the latter containing the
partition layout data. It can be accessed via the "String expansion"
mechanism.
Previous versions of mpp would already set the arch and basearch
substitution, which would work for dep-solving itself, but not
properly re-write the resulting URLs which means that the manifest
was broken. Fix this by properly replacing the substitutions in
the URL. Also support official 'releasever' substitution.
Instead of passing dictionaries around that are inconvenient to
use in code and even more in the `mpp-format-*` directives, use
a simple class to represent package information. Use that in
the `pkginfo` dict that can be accessed via `mpp-format-*`. Use
the `evra` property instead of string manipulation in the
`fedora-boot.mpp.json` and `-ostree-bootiso.mpp.json` manifest.
