ipatests: clear initgroups cache in clear_sssd_cache
The tasks module provides a method to clear sssd cache,
but the method does not remove the file /var/lib/sss/mc/initgroups.
Update the method to also remove this file.
Signed-off-by: Florence Blanc-Renaud <flo@redhat.com>
Reviewed-By: Rob Crittenden <rcritten@redhat.com>