move test artifact build rules into open source location

Bug: 29404304
Change-Id: I5553d275fe478fac0d6fe00a931a1c1f1e3bdd59
(cherry picked from commit 8322be725282d4ac64a65b44e2f6b0c681e35819)
diff --git a/core/Makefile b/core/Makefile
index 37bad8a..02bd4f7 100644
--- a/core/Makefile
+++ b/core/Makefile
@@ -2267,6 +2267,8 @@
 -include $(sort $(wildcard vendor/*/*/build/tasks/*.mk))
 -include $(sort $(wildcard device/*/*/build/tasks/*.mk))
 -include $(sort $(wildcard product/*/*/build/tasks/*.mk))
+# Also add test specifc tasks
+include $(sort $(wildcard platform_testing/build/tasks/*.mk))
 endif
 
 include $(BUILD_SYSTEM)/product-graph.mk