Open the PAC socket from krb5_child before dropping root
The PAC responder by default allows only connections from the root user.
This patch opens the socket to the PAC responder before the krb5_child
drops privileges so the connection seemingly comes from root.
https://fedorahosted.org/sssd/ticket/2559
Reviewed-by: Sumit Bose <sbose@redhat.com>