✅ Fix create resubmit test

One of our tests currently checks resubmitting a create op after
reconnecting during submission.

However, since reconnection happens so quickly, this test case can cause
two commit attempts in parallel.

We currently only wait for the first request to resolve, which means
that the second request can continue into the next test, causing
unexpected test failures.

This change waits for both acks to be sent before finishing the test.

test/client/submit.js

@@ -289,11 +289,15 @@ module.exports = function() {
             next();
           });
 
-          var doc = connection.get('dogs', 'fido');
-          doc.create({age: 3}, function(error) {
-            expect(doc.version).to.equal(1);
-            done(error);
+          var count = 0;
+          backend.use('reply', function(message, next) {
+            next();
+            if (message.reply.a === 'op') count++;
+            if (count === 2) done();
           });
+
+          var doc = connection.get('dogs', 'fido');
+          doc.create({age: 10}, errorHandler(done));
         });
 
         it('does not fail when resubmitting a create op on a doc that was deleted', function(done) {