test: fix assert in test-http-outgoing-finish

Given the assert message, and the fact that endCb is always true
in the assert, I am pretty sure the test author was intending
to test for finishEvent, not endCb.

test/simple/test-http-outgoing-finish.js

@@ -69,7 +69,7 @@ function write(out) {
     endCb = true;
     console.error('%s endCb', name);
     process.nextTick(function() {
-      assert(endCb, name + ' got endCb event before finishEvent!');
+      assert(finishEvent, name + ' got endCb event before finishEvent!');
       console.log('ok - %s endCb', name);
     });
   });