ipatests: fix the method adding ifp to sssd.conf
The test TestCertsInIDOverrides enables the ifp service in
sssd.conf by a sed command. If the service is already enabled,
the ifp service appears multiple times in the section
[sssd]
services = ..ifp...ifp
and sssd fails to start.
Use tasks.remote_sssd_config to properly configure the
services as this API properly handles the case when the
service is already configured.
Fixes: https://pagure.io/freeipa/issue/8371
Reviewed-By: Anuja More <amore@redhat.com>
Reviewed-By: Rob Crittenden <rcritten@redhat.com>