[test] call $timeout.flush() before debounce tests

* Otherwise, the '$http GET' to fetch translation resources
shows up as a deferred task here.

* Referenced from:
srl295@5d9959c

src/ui/public/debounce/__tests__/debounce.js

@@ -15,6 +15,9 @@ function init() {
     $timeoutSpy = sinon.spy($timeout);
 
     debounce = $injector.get('debounce');
+
+    // ensure there is a clean slate before testing deferred tasks
+    $timeout.flush();
   });
 }