dns: Handle SERVFAIL in check if domain already exists.

In cases where domain is already delegated to IPA prior installation
we might get timeout or SERVFAIL. The answer depends on the recursive
server we are using for the check.

Reviewed-By: David Kupka <dkupka@redhat.com>

ipaserver/install/dns.py

@@ -126,10 +126,12 @@ def install_check(standalone, replica, options, hostname):
         domain = dnsutil.DNSName(util.normalize_zone(api.env.domain))
         print("Checking DNS domain %s, please wait ..." % domain)
         try:
-            ipautil.check_zone_overlap(domain, raise_on_timeout=False)
+            ipautil.check_zone_overlap(domain, raise_on_error=False)
         except ValueError as e:
             if options.force or options.allow_zone_overlap:
-                root_logger.warning(e.message)
+                root_logger.warning("%s Please make sure that the domain is "
+                                    "properly delegated to this IPA server.",
+                                    e.message)
             else:
                 raise e