Populate krb_principal_name from GSS_NAME env var
mod_auth_gssapi provides by default the local name in
REMOTE_USER and the full principal in GSS_NAME. Grab a
copy of that principal for krb_principal_name.
https://fedorahosted.org/ipsilon/ticket/115
Signed-off-by: Rob Crittenden <rcritten@redhat.com>
Reviewed-by: Simo Sorce <simo@redhat.com>