Follow change to ART_TEST_LIST_*

ART_TEST_LIST_* now contain full paths instead of paths relative
to $(OUT_DIR).

Test: m checkbuild
Change-Id: Id4d8610bfd93eb0b9080e83f05b878aedab0967e
diff --git a/build/art.go b/build/art.go
index 31de57f..56eec54 100644
--- a/build/art.go
+++ b/build/art.go
@@ -276,7 +276,7 @@
 	defer artTestMutex.Unlock()
 
 	tests := testMap[name]
-	tests = append(tests, ctx.Path().RelPathString())
+	tests = append(tests, ctx.Path().ToMakePath().String())
 	testMap[name] = tests
 }