Create ArtifactPath function to abstract test paths

When AOS is included as an external repo and renamed, paths have to be
updated.  Make a function to handle all this.

Change-Id: If1dfbfb3191809d86da1dca92981b7a0b851c51f
diff --git a/aos/actions/action_test.cc b/aos/actions/action_test.cc
index 565bf11..1c8e506 100644
--- a/aos/actions/action_test.cc
+++ b/aos/actions/action_test.cc
@@ -11,6 +11,7 @@
 #include "aos/actions/actor.h"
 #include "aos/actions/test_action_generated.h"
 #include "aos/events/simulated_event_loop.h"
+#include "aos/testing/path.h"
 
 namespace aos {
 namespace common {
@@ -97,8 +98,8 @@
 class ActionTest : public ::testing::Test {
  protected:
   ActionTest()
-      : configuration_(
-            configuration::ReadConfig("aos/actions/action_test_config.json")),
+      : configuration_(configuration::ReadConfig(
+            aos::testing::ArtifactPath("aos/actions/action_test_config.json"))),
         event_loop_factory_(&configuration_.message()),
         actor1_event_loop_(event_loop_factory_.MakeEventLoop("actor1")),
         actor2_event_loop_(event_loop_factory_.MakeEventLoop("actor2")),