Revert "Revert "More Makefile fun for --debuggable.""

This reverts commit 9728a930fdf717cca60b48d9c2b715d0eed497fd.

Change-Id: Ieca964a793e58f11931f78f50be47a4a9f0dc21f
diff --git a/build/Android.common_test.mk b/build/Android.common_test.mk
index 547e92e..b536fe4 100644
--- a/build/Android.common_test.mk
+++ b/build/Android.common_test.mk
@@ -100,6 +100,9 @@
 # Do you want failed tests to have their artifacts cleaned up?
 ART_TEST_RUN_TEST_ALWAYS_CLEAN ?= true
 
+# Do you want run-tests with the --debuggable flag
+ART_TEST_RUN_TEST_DEBUGGABLE ?= $(ART_TEST_FULL)
+
 # Define the command run on test failure. $(1) is the name of the test. Executed by the shell.
 define ART_TEST_FAILED
   ( [ -f $(ART_HOST_TEST_DIR)/skipped/$(1) ] || \