Reduce level of 'could not run' messages info->debug

We expect not to find all commands; don't output a log message on
each missing binary.

Signed-off-by: Bryn M. Reeves <bmr@redhat.com>
Fix policy classes for --tmp-dir

Policy classes need to return the user-supplied temporary
directory if they decide not to override it.

Signed-off-by: Bryn M. Reeves <bmr@redhat.com>