ui: Default test latency to 0 (#8640)

During development a HTTP request will pause for 1 minute ONLY when an
?index is set. This gives a realistic emulation of blocking queries.

During testing we can change this latency when we are testing blocking
queries, which we do in numerous places.

A problem can arise during testing on a very slow machine.

If you are not testing blocking queries and therefore not set a latency
to test with, if the machine you are testing on is slow enough a normal
page can assert during a test, yet not tear down before a further
blocking query request is made. This blocking query then uses the default
latency which cause the page to hang for 1 minute, which in turn causes
the test to timeout.

This only seems to happen on a very slow system, but it does potentially
explain why we occasionally see the odd flakey test popping up.

ui-v2/tests/helpers/yadda-annotations.js

@@ -18,6 +18,9 @@ const reset = function() {
     list.add(item);
   });
 };
+const startup = function() {
+  api.server.setCookie('CONSUL_LATENCY', 0);
+};
 
 const runTest = function(context, libraries, steps, scenarioContext) {
   return new Promise((resolve, reject) => {
@@ -89,6 +92,9 @@ export const setupFeature = function(featureAnnotations) {
 };
 export const setupScenario = function(featureAnnotations, scenarioAnnotations) {
   return function(model) {
+    model.beforeEach(function() {
+      startup();
+    });
     model.afterEach(function() {
       reset();
     });