Fix more unit tests. (#1406)

- Randomise test order.
- Use deferred fulfilment in more places.
- Make sure to change something before awaiting the fulfilment.
- Build a fresh AppSettings after reset().
- Retry tests on failure.

UnitTests/SupportingFiles/UnitTests.xctestplan

@@ -16,6 +16,7 @@
         "value" : "1"
       }
     ],
+    "testExecutionOrdering" : "random",
     "testTimeoutsEnabled" : true
   },
   "testTargets" : [