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/BUILD b/aos/BUILD
index 04293df..0c94f35 100644
--- a/aos/BUILD
+++ b/aos/BUILD
@@ -355,6 +355,7 @@
         ":json_to_flatbuffer",
         ":json_to_flatbuffer_fbs",
         "//aos/testing:googletest",
+        "//aos/testing:path",
     ],
 )
 
@@ -371,6 +372,7 @@
         ":json_to_flatbuffer",
         ":json_to_flatbuffer_fbs",
         "//aos/testing:googletest",
+        "//aos/testing:path",
         "//aos/util:file",
         "@com_github_google_flatbuffers//:flatbuffers",
     ],
@@ -439,6 +441,7 @@
         ":configuration",
         "//aos/testing:flatbuffer_eq",
         "//aos/testing:googletest",
+        "//aos/testing:path",
         "//aos/testing:test_logging",
     ],
 )