FM-1509 Update for Future_Parser Testing

Sorry - I don't have any issue with the env var, nor do I disagree with the concerns for dupe config files.

I was more concerned with where the env var gets read / how it's passed in to configure the tests.  FWIW, I prefer such config to be read as high in the call stack as possible if that makes sense.

That's why I asked where `#{master}` comes from as this isn't a `def` in the current class, nor is the module `Systest::Util::Registry` derived from any other.  So I presume that if there's state that has been injected into this class that there's already a mechanism for configuring the module?  Whatever that mechanism is should be the same one used to configure future parser.