test: make stdout-close-unref work in test runner

process.stdout isn't fully initialized yet by the time the test starts
when invoked with `python tools/test.py`. Use process.stdin instead and
force initialization with process.stdin.resume().

test/simple/test-stdout-close-unref.js

@@ -19,5 +19,6 @@
 // OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE
 // USE OR OTHER DEALINGS IN THE SOFTWARE.
 
-process.stdout._handle.close();
-process.stdout._handle.unref();  // Should not segfault.
+process.stdin.resume();
+process.stdin._handle.close();
+process.stdin._handle.unref();  // Should not segfault.