Use PRODUCT_OUT instead of ANDROID_PRODUCT_OUT

This fixes an error when running art/tools/buildbot-build.sh:
art/Android.mk:137: error: ANDROID_PRODUCT_OUT is obsolete. Use
PRODUCT_OUT instead.

Test: successfully executed buildbot-build.sh
Change-Id: If269bb7b5b53c2940b4299c953f8fd9c27dc2c50
1 file changed