(FACT-2512) Handle Raspbian as Debian

[mlove-au]

This change makes facter run on a Raspbian distro.

The new os facts reported:

os => {
  architecture => "armv7l",
  distro => {
    codename => "stretch",
    description => "Raspbian GNU/Linux 9.11 (stretch)",
    id => "Raspbian",
    release => {
      full => "9.11",
      major => "9",
      minor => "11"
    }
  },
  family => "Debian",
  hardware => "armv7l",
  name => "Raspbian",
  release => {
    full => "9.11",
    major => "9",
    minor => "11"
  },
  selinux => {
    enabled => false
  }
}