Univention Corporate Server 4.2 erratum 165 (security)

This update addresses the following issue(s):
* Some code path don't enforce smb signing, when they should (CVE-2017-12150)
* Keep required encryption across SMB3 dfs redirects (CVE-2017-12151)
* Client with write access to a share can cause server memory contents to be
  written into a file or printer (CVE-2017-12163)
* Samba tool sysvolreset logs ACL operation errors instead of aborting.
* Samba tool sysvolcheck does not longer check the netlogon share.
* Samba tools regarding the creation of users with User Principal
  Names have been fixed.