Add ApiDemos to the test build, and cts-permission2 tests to test_defs.xml.

This should enable the ApiDemos sample tests to run continuously again.
diff --git a/samples/ApiDemos/Android.mk b/samples/ApiDemos/Android.mk
index e10ef43..7921120 100644
--- a/samples/ApiDemos/Android.mk
+++ b/samples/ApiDemos/Android.mk
@@ -1,7 +1,7 @@
 LOCAL_PATH:= $(call my-dir)
 include $(CLEAR_VARS)
 
-LOCAL_MODULE_TAGS := samples
+LOCAL_MODULE_TAGS := samples tests
 
 # Only compile source java files in this apk.
 LOCAL_SRC_FILES := $(call all-java-files-under, src)