ipaserver/dcerpc: Ensure LSA pipe has session key before using it
With Samba 4.2 there is a bug that prevents Samba to consider Kerberos
credentials used by IPA httpd process when talking to smbd. As result,
LSA RPC connection is seen as anonymous by Samba client code and we cannot
derive session key to use for encrypting trust secrets before transmitting
them.
Additionally, rewrite of the SMB protocol support in Samba caused previously
working logic of choosing DCE RPC binding string to fail. We need to try
a different set of priorities until they fail or succeed.
Requires Samba fixes from https://bugzilla.redhat.com/show_bug.cgi?id=1219832
Fixes https://bugzilla.redhat.com/show_bug.cgi?id=1219834
Reviewed-By: Tomas Babej <tbabej@redhat.com>