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

install/tools/ipa-dns-install

@@ -223,7 +223,7 @@ def main():
                zone_notif=options.zone_notif)
     bind.create_instance()
 
-    # Restart http instance to make sure acutil has the right resolver
+    # Restart http instance to make sure that python-dns has the right resolver
     # https://bugzilla.redhat.com/show_bug.cgi?id=800368
     http = httpinstance.HTTPInstance(fstore)
     service.print_msg("Restarting the web server")