Explicitly pass down ccache names for connections
    
    Instead of relying on side effects (setting the KRB5CCNAME env var),
    explicitly pass the ccache name to be used if it is not the default
    ccache. This fixes some tests that sometimes fail to work properly due
    to the wrong ccache being used.
    
    https://fedorahosted.org/freeipa/ticket/6543
    
    Signed-off-by: Simo Sorce <simo@redhat.com>
    Reviewed-By: Jan Cholasta <jcholast@redhat.com>