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/events/logging/logger_test.cc b/aos/events/logging/logger_test.cc
index 4b0f375..a342c12 100644
--- a/aos/events/logging/logger_test.cc
+++ b/aos/events/logging/logger_test.cc
@@ -12,6 +12,7 @@
 #include "aos/network/remote_message_generated.h"
 #include "aos/network/testing_time_converter.h"
 #include "aos/network/timestamp_generated.h"
+#include "aos/testing/path.h"
 #include "aos/testing/tmpdir.h"
 #include "aos/util/file.h"
 #include "glog/logging.h"
@@ -26,6 +27,8 @@
 namespace logger {
 namespace testing {
 
+using aos::testing::ArtifactPath;
+
 namespace chrono = std::chrono;
 using aos::message_bridge::RemoteMessage;
 using aos::testing::MessageCounter;
@@ -51,8 +54,8 @@
 class LoggerTest : public ::testing::Test {
  public:
   LoggerTest()
-      : config_(
-            aos::configuration::ReadConfig("aos/events/pingpong_config.json")),
+      : config_(aos::configuration::ReadConfig(
+            ArtifactPath("aos/events/pingpong_config.json"))),
         event_loop_factory_(&config_.message()),
         ping_event_loop_(event_loop_factory_.MakeEventLoop("ping")),
         ping_(ping_event_loop_.get()),
@@ -427,8 +430,8 @@
 class MultinodeLoggerTest : public ::testing::TestWithParam<struct Param> {
  public:
   MultinodeLoggerTest()
-      : config_(aos::configuration::ReadConfig(
-            absl::StrCat("aos/events/logging/", GetParam().config))),
+      : config_(aos::configuration::ReadConfig(ArtifactPath(
+            absl::StrCat("aos/events/logging/", GetParam().config)))),
         time_converter_(configuration::NodesCount(&config_.message())),
         event_loop_factory_(&config_.message()),
         pi1_(