rootfs: Add in Debian security apt lists

Change-Id: I6ea9d10db1513f72ff4ba500857add5c839060b9
diff --git a/rootfs.mk b/rootfs.mk
index 09235d3..d9dea5b 100644
--- a/rootfs.mk
+++ b/rootfs.mk
@@ -158,6 +158,8 @@
 	sudo mkdir -p $(ROOTFS_DIR)/opt/aiy
 	sudo tar -xvf $(ROOTDIR)/cache/packages.tgz -C $(ROOTFS_DIR)/opt/aiy/
 endif
+	echo 'deb https://deb.debian.org/debian-security/ stretch/updates main' |sudo tee $(ROOTFS_DIR)/etc/apt/sources.list.d/security.list
+	echo 'deb-src https://deb.debian.org/debian-security/ stretch/updates main' |sudo tee -a $(ROOTFS_DIR)/etc/apt/sources.list.d/security.list
 	sudo cp $(ROOTDIR)/build/99network-settings $(ROOTFS_DIR)/etc/apt/apt.conf.d/
 	sudo chroot $(ROOTFS_DIR) bash -c 'apt-get update'
 	sudo chroot $(ROOTFS_DIR) bash -c 'apt-get install -y --allow-unauthenticated aiy-board-keyring'