Please don't use this setting in a production system but in some
environments it is needed for completely automated *testing* to be able
to use ssh correctly.
make the arguments optional (with documented defaults) plus they need
not exist a priori, reducing one command (the silly mkdir!) that the
user has to run.
All this is preparatory to deprecating the from-client method. We've
even switched the test suite to 'non-root' method now
