Make --test use the native scheduler

[brson]

Using the green scheduler by default for testing results in some unexpected differences in behavior, particularly when performance is different under testing than not.

Nominating because it will be harder to change this post 1.0.

[alexcrichton]

The native scheduler is actually currently the default, yay easy issues to close!

[brson]

\o/ Should have put it on the milestone first to get those stats up.