improved error message for kerberos authentication when KDC cannot be resolved

to use samba tools with kerberos, the SRV record for _kerberos needs to be resolvable.
when this isn't the case, the error message indicated an unspecific logon failure.
improve the message and point the user to check DNS settings or setup the config file /etc/krb5.conf.

Author: exploide

enum4linux-ng.py

@@ -545,6 +545,9 @@ def run(self, log, error_filter=True):
                 output = output.replace(line, "")
         output = output.rstrip('\n')
 
+        if "Cannot find KDC for realm" in output:
+            return Result(False, "Cannot find KDC for realm, check DNS settings or setup /etc/krb5.conf")
+
         if retval == 1 and not output:
             return Result(False, "empty response")