Update test_roles.py
    
    Import file as of commit ad78e76d475960bd0a86c646734a40a98c79a6d9 in
    OPS-Service/salt.git.
    
    Noteable changes:
    - allow nested roles, i.e. roles in subdirectories - this allows for
      better grouping of related roles
    
    Signed-off-by: Georg Pfuetzenreuter <georg.pfuetzenreuter@suse.com>