admin module for user/group/permissions cleanup

Users/groups/perms are meant to be defined in yaml.

Applied like:

yaml:

  groups:
    test1:
      gid: 1
      members: [foo]
    test2:
      gid: 2
      members: []

  users:
    foo:
      uid: 1
      ...

.pp
  node /foo/ {
    #groups create their users (can overlap) and permissions
    #as well as system groups and handling user membership
    class { 'admin': groups => ['test', 'test2'], }
  }

More info see: admin/README

Change-Id: I6982bfced50a22faac37246dff4d52ff163a34ed