provide dedicated ccache file for httpd
    
    httpd service stores Kerberos credentials in kernel keyring which gets
    destroyed and recreated during service install/upgrade, causing problems when
    the process is run under SELinux context other than 'unconfined_t'. This patch
    enables HTTPInstance to set up a dedicated CCache file for Apache to store
    credentials.
    
    https://fedorahosted.org/freeipa/ticket/4973
    
    Reviewed-By: Jan Cholasta <jcholast@redhat.com>
    Reviewed-By: Alexander Bokovoy <abokovoy@redhat.com>