Don't redirect output in rustpkg test

Previously, if tests failed, you'd only get stderr which isn't very
useful, especially if the failure didn't happen directly in a test
function (e.g None.unwrap()).
auto merge of #9603 : sfackler/rust/rustpkg-test, r=catamorphism

Previously, if tests failed, you'd only get stderr which isn't very
useful, especially if the failure didn't happen directly in a test
function (e.g None.unwrap()).