Add automatic retry to the Firestore tests (#652)

Author: a-maurice

firestore/testapp/Assets/Firebase/Sample/Firestore/UIHandlerAutomated.cs

@@ -177,7 +177,8 @@ protected override void Start() {
 
       testRunner = AutomatedTestRunner.CreateTestRunner(
         testsToRun: testFilter.Length > 0 ? testFilter : tests,
-        logFunc: LogInBatches
+        logFunc: LogInBatches,
+        maxAttempts: 3
       );
 
       Debug.Log("NOTE: Some API calls report failures using UnityEngine.Debug.LogError which will " +