Misc bits: dual package system support

• We had the means to allow installing rpms unmodified to our ProdNG deb image, and even have them update the dpkg file list.

• We however opted for not adding that complexity since dual package support would have rough edges and unfortunate side effects.

• We also wanted to entice our internal developers to just switch to a single system to make things simpler: debs for all.

• As a result, we were able to drop another 4MB or so of packages just for RPM support.

• rpm2cpio itself requires 3-4MB of dependencies, but it can be rewritten as a small shell script :)