Add "nodpi" to DpiTest Android.mk

Part of the drawables for DpiTest is a nodpi directory, but the
LOCAL_AAPT_FLAGS didn't specify it.

Bug: 3165492
Change-Id: I989068d76f922db6048e6db7cc6822ab3234d36e
diff --git a/tests/DpiTest/Android.mk b/tests/DpiTest/Android.mk
index 5463a17..f55ce6e 100644
--- a/tests/DpiTest/Android.mk
+++ b/tests/DpiTest/Android.mk
@@ -7,6 +7,6 @@
 
 LOCAL_MODULE_TAGS := tests
 
-LOCAL_AAPT_FLAGS = -c 120dpi -c 240dpi -c 160dpi
+LOCAL_AAPT_FLAGS = -c 120dpi,240dpi,160dpi,nodpi
 
 include $(BUILD_PACKAGE)