krb5-child: add revert_changepw_options()
After changing the Kerberos password krb5-child will try to get a fresh
TGT with the new password. This patch tries to make sure the right gic
options are used.
Resolves: https://fedorahosted.org/sssd/ticket/2289
Reviewed-by: Jakub Hrozek <jhrozek@redhat.com>