Prevent flooding of meaningless traceback in sanic_endpoint_test

When Sanic has an exception in a request middleware, it fails to
save request object in `results`. In `sanic_endpoint_test`, because
it always requires `results` to have both `request` and `response` objects,
it prints traceback like attached example. It is not a user code and
it doesn't give any information to users, it is better to suppress
to print this kind of error.

To fix it, this patch insert collect hook as first request middleware
to guarantee to successfully run it always.

```
app = <sanic.sanic.Sanic object at 0x1102b5358>, method = 'get', uri = '/ping/', gather_request = True, loop = None
debug = True, request_args = (), request_kwargs = {}
_collect_request = <function sanic_endpoint_test.<locals>._collect_request at 0x11286c158>
_collect_response = <function sanic_endpoint_test.<locals>._collect_response at 0x11286c378>

    def sanic_endpoint_test(app, method='get', uri='/', gather_request=True,
                            loop=None, debug=False, *request_args,
                            **request_kwargs):
        results = []
        exceptions = []

        if gather_request:
            @app.middleware
            def _collect_request(request):
                results.append(request)

        async def _collect_response(sanic, loop):
            try:
                response = await local_request(method, uri, *request_args,
                                               **request_kwargs)
                results.append(response)
            except Exception as e:
                exceptions.append(e)
            app.stop()

        app.run(host=HOST, debug=debug, port=42101,
                after_start=_collect_response, loop=loop)

        if exceptions:
            raise ValueError("Exception during request: {}".format(exceptions))

        if gather_request:
            try:
>               request, response = results
E               ValueError: not enough values to unpack (expected 2, got 1)

../sanic/sanic/utils.py:46: ValueError
```

sanic/utils.py

@@ -22,9 +22,9 @@ def sanic_endpoint_test(app, method='get', uri='/', gather_request=True,
     exceptions = []
 
     if gather_request:
-        @app.middleware
         def _collect_request(request):
             results.append(request)
+        app.request_middleware.appendleft(_collect_request)
 
     async def _collect_response(sanic, loop):
         try: