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

ipa-client/ipaclient/ntpconf.py

@@ -133,7 +133,7 @@ def config_ntp(server_fqdn, fstore = None, sysstore = None):
     # Restart ntpd
     ipaservices.knownservices.ntpd.restart()
 
-def synconce_ntp(server_fqdn):
+def synconce_ntp(server_fqdn, debug=False):
     """
     Syncs time with specified server using ntpdate.
     Primarily designed to be used before Kerberos setup
@@ -142,15 +142,17 @@ def synconce_ntp(server_fqdn):
     Returns True if sync was successful
     """
     ntpdate="/usr/sbin/ntpdate"
-    result = False
     if os.path.exists(ntpdate):
         # retry several times -- logic follows /etc/init.d/ntpdate
         # implementation
+        cmd = [ntpdate, "-U", "ntp", "-s", "-b"]
+        if debug:
+            cmd.append('-d')
+        cmd.append(server_fqdn)
         for retry in range(0,3):
             try:
-                ipautil.run([ntpdate, "-U", "ntp", "-s", "-b", server_fqdn])
-                result = True
-                break
+                ipautil.run(cmd)
+                return True
             except:
                 pass
-    return result
+    return False