SECRETS: Store ccaches in secrets for the KCM responder
    
    Adds a new "hive" to the secrets responder whose base path is /kcm. Only
    root can contact the /kcm hive, because the KCM responder only runs as
    root and it must impersonate other users and store ccaches on their behalf.
    
    Reviewed-by: Michal Židek <mzidek@redhat.com>
    Reviewed-by: Simo Sorce <simo@redhat.com>