We force the hostname in `kitchen` so the `_mapdata` files can be
static.

The `system.hostname` return the result of either `hostname -s` or
`hostnamectl --static` depending of the availability of each command.

The `system.platform` return a hash with tweaked `inspec.platform`
values:

- `system.platform[:family]` provides a family name for Arch
- `system.platform[:name]` modify `amazon` to `amazonlinux`
- `system.platform[:release]` tweak for Arch and Amazon Linux:
  - `Arch` is always `base-later`
  - `Amazon Linux` release `2018` became `1`
- `system.platform[:finger]` is just the concatenation of the name and
  the first release number (except for Ubuntu which gives `20.04` for
  example)