Use zypper to download/install kernel rpms instead of doing it manually

[marcosps]

klp-build downloads packages using osc-tiny, then it extracts the rpms into specific directories. zypper can do exactly that, with only one tool: we can specify the repositories that we want to download the packages and the directory we want it to be installed, and that's it.

I'm not sure if there are other caveats or problems to switch to zypper, but we should try switching to it.

[marcosps]

Maybe installing the rpm package using zypper can be tricky, but only downloading the packages can be done (IHMO), we just need to figure it out how to pass a repo for it to check.