Run prepare and package in containers

[Eeems]

Currently, prepare and package are run on the host system, this means that there is no way to ensure that different commands are actually available. This makes package recipes not fully portable between distributions.

It would probably make sense to run in the same container that build runs in, and that way we can make use of makedepends to add needed dependencies.

[Eeems]

Running package in a container could be problematic when it comes to creating the final package, as the prepare step may change ownership of the file, and the uid/gid would not match the main system when it's run. As such it doesn't make sense to run the package script in a container yet. It may make more sense to package a busybox runtime with toltecmk that it uses for the prepare step instead of the system environment, and run that in a chroot instead.

[Eeems]

Split out to #64

[Eeems]

Related #13