Fix flaky test TestCompareTraceQueryResponse

The test occasionally fails with:

```
Received unexpected error:
http get: Get "http://localhost:9201/api/services": dial tcp [::1]:9201: connect: connection refused
```

The server listen and client connect, which run in separate goroutines,
race against one another. Occasionally, the client connect is faster
than the server listen, causing the above error.

By moving the call to `net.Listen` out of the goroutine, we ensure that
both threads of execution must wait on the socket listen to complete
before proceeding, eliminating the race.

Author: JamesGuthrie

pkg/tests/end_to_end_tests/trace_query_integration_test.go

@@ -102,15 +102,18 @@ func TestCompareTraceQueryResponse(t *testing.T) {
 		jaegerQuery := jaegerquery.New(pgxconn.NewPgxConn(db), &jaegerquery.DefaultConfig)
 		promscaleJaeger.ExtendQueryAPIs(router, pgxconn.NewPgxConn(db), jaegerQuery)
 
+		// Bind to the server port. This must be outside of the goroutine below
+		// to prevent the server bind and client connect from racing.
+		listener, err := net.Listen("tcp", ":0")
+		require.NoError(t, err)
+
 		go func() {
-			listener, err := net.Listen("tcp", ":9201")
-			require.NoError(t, err)
 			server := http.Server{Handler: router}
 			require.NoError(t, server.Serve(listener))
 		}()
 
 		// Create client for querying and comparing results.
-		promscaleClient := httpClient{"http://localhost:9201"}
+		promscaleClient := httpClient{"http://" + listener.Addr().String()}
 		jaegerResponse, err := loadJaegerQueryResponses()
 		require.NoError(t, err)