allow minimal amount of failing tests for Perl

A handful of individual tests sometimes fail for Perl, usually because of locale settings.

The PR allows that less than 1% of the tests fail, and also makes sure `make test` is always run (except when `runtest` is explicitly set to `False`.
the `log_all` needs to be `False` in order to capture the exit code ourselves

I'll try setting the locale hard though, rather than allowing individual tests to fai.