Don't configure KEYRING ccache in containers
    
    Kernel keyrings are not namespaced yet. Keyrings can leak into other
    containers. Therefore keyrings should not be used in containerized
    environment.
    
    Don't configure Kerberos to use KEYRING ccache backen when a container
    environment is detected by systemd-detect-virt --container.
    
    Fixes: https://pagure.io/freeipa/issue/7807
    Signed-off-by: Christian Heimes <cheimes@redhat.com>
    Reviewed-By: Rob Crittenden <rcritten@redhat.com>
    Reviewed-By: Tibor Dudlak <tdudlak@redhat.com>
    Reviewed-By: Oleg Kozlov <okozlov@redhat.com>