s3-libsmb: Do not look up FQDN or use host/ for krb5 encrypted CIFS

s3-libsmb: Do not look up FQDN or use host/ for krb5 encrypted CIFS

This is important, as we want to use exactly the same name and ticket
that the libsmb session setup code used, so we do not hit the KDC twice.

For the session setup to have succeded using the default 'client use
spnego principal = no', the cifs/ principal must exist anyway, so
looking for host/ is pointless.  The case of 'client use spnego
principal = yes' was never supported here.

Andrew Bartlett