test: introduce common.crashOnUnhandledRejection

Ref: #12442
PR-URL: #12489
Reviewed-By: Matthew Loring <mattloring@google.com>
Reviewed-By: Julien Gilli <jgilli@nodejs.org>
Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

test/common.js

@@ -677,3 +677,9 @@ exports.getArrayBufferViews = function getArrayBufferViews(buf) {
   }
   return out;
 };
+
+// Crash the process on unhandled rejections.
+exports.crashOnUnhandledRejection = function() {
+  process.on('unhandledRejection',
+             (err) => process.nextTick(() => { throw err; }));
+};