Replace DNS client based on acutil with python-dns
    
    IPA client and server tool set used authconfig acutil module to
    for client DNS operations. This is not optimal DNS interface for
    several reasons:
    - does not provide native Python object oriented interface
      but but rather C-like interface based on functions and
      structures which is not easy to use and extend
    - acutil is not meant to be used by third parties besides
      authconfig and thus can break without notice
    
    Replace the acutil with python-dns package which has a feature rich
    interface for dealing with all different aspects of DNS including
    DNSSEC. The main target of this patch is to replace all uses of
    acutil DNS library with a use python-dns. In most cases, even
    though the larger parts of the code are changed, the actual
    functionality is changed only in the following cases:
    - redundant DNS checks were removed from verify_fqdn function
      in installutils to make the whole DNS check simpler and
      less error-prone. Logging was improves for the remaining
      checks
    - improved logging for ipa-client-install DNS discovery
    
    https://fedorahosted.org/freeipa/ticket/2730
    https://fedorahosted.org/freeipa/ticket/1837