ipautil: use file in a temporary dir as ccache in private_ccache
    
    python-gssapi chokes on empty ccache files, so instead of creating an empty
    temporary ccache file in private_ccache, create a temporary directory and
    use a non-existent file in that directory as the ccache.
    
    https://fedorahosted.org/freeipa/ticket/5401
    
    Reviewed-By: Martin Basti <mbasti@redhat.com>
    Reviewed-By: Simo Sorce <ssorce@redhat.com>