Smoother concurrent test-flow

The noop trick initializes the STDOUT, so that the TAP::Harness
issued IO::Select->can_read calls (which are blocking wtf wtf wtf)
keep spinning and scheduling jobs

This results in an overall much smoother job-queue drainage, since
the Harness blocks less

(ideally this needs to be addressed in T::H, but a quick patchjob
broke everything so tabling it for now)
Remove anything preinstalled on the travis perls when CLEANTEST is true

This will give us yet another test point