ipaplatform: Add Debian platform module.
    
    v2:
    - use redhat_services.redhat_system_units.copy
    - don't use wildcard imports
    - add some empty lines to make pep8 happy
    
    v3:
    - make parse_ipa_version static
    
    v4:
    - make more methods static
    
    v5:
    - fix pylint issues
    - use syntax that doesn't break with python3
    
    v6:
    - remove IPA_GETKEYTAB from paths, it's the same across distros
    
    Reviewed-By: Stanislav Laznicka <slaznick@redhat.com>
    Reviewed-By: Christian Heimes <cheimes@redhat.com>