Test: Use unique mocked utils for each test

The mocked utils object was shared between the tests because it's a
static object. This causes problems on expecting the number of
called the mocked functions.

Add a freeUtils() in mocked_utils.hpp, and call it in test fixture's
destructor, so that each test case will use a different mocked object.

Signed-off-by: Lei YU <mine260309@gmail.com>
Change-Id: I2622c678012d30b2bd75dc37a2bc3a663f40d86c
diff --git a/test/test_item_updater.cpp b/test/test_item_updater.cpp
index fb6ea93..ed55906 100644
--- a/test/test_item_updater.cpp
+++ b/test/test_item_updater.cpp
@@ -32,6 +32,7 @@
 
     ~TestItemUpdater()
     {
+        utils::freeUtils();
     }
 
     const auto& GetActivations()