SASL bind callback due to refactoring was referencing local variable which
didn't exist all the time. Fix that by including a copy of service principals
into ipasam long term private struct.
Rework ccache handling to avoid re-initing every time callback is called
Samba just needs the cifs/ key on the ipa server. Configure samba to use a
different keytab file so that we do not risk samba commands (net, or similar)
to mess up the system keytab.
https://fedorahosted.org/freeipa/ticket/2168
