Improvements and bugfixes for Kerberos-only environments

[SimonWessling]

When using smartbrute with Kerberos authentication, smartbrute tries to look up the KDC hostname (get_machine_name()), which it requires to construct the SPN, via SMB anonymous login. This leads to an unhandled exception in environments where NTLM authentication is disabled. I added a command line argument --dc-host to specify the KDC host directly, eliminating the lookup via SMB. This is similar to the approach taken in some impacket example scripts.

While I was at it, I also fixed a small bug and added a hint to use --use-ldaps when Kerberos login over plain LDAP fails.

[ShutdownRepo]

Thank you for this addition, can you resolve the conflicts that probably raised with the last merge?