mod_auth_gssapi: enable unique credential caches names
    
    mod_auth_gssapi > 1.4.0 implements support for unique ccaches names.
    Without it ccache name is derived from pricipal name.
    
    It solves a race condition in two concurrent request of the same
    principal. Where first request deletes the ccache and the second
    tries to use it which then fails. It may lead e.g. to a failure of
    two concurrent ipa-client-install.
    
    With this feature there are two ccaches so there is no clash.
    
    https://fedorahosted.org/freeipa/ticket/5653
    
    Reviewed-By: Stanislav Laznicka <slaznick@redhat.com>
    Reviewed-By: Robbie Harwood <rharwood@redhat.com>