Make sure Android package is constructed from top build dir

scripts/create-package.sh

@@ -1,8 +1,9 @@
 #!/bin/bash
 
-TOPDIR=`pwd`
+TOPDIR=`echo $ANDROID_BUILD_TOP`
 PRODUCT_NAME=generic_arm64
 OUTDIR=out/target/product/$PRODUCT_NAME
+CURDIR=`pwd`
 
 if [ -d rootfs ] ; then
 	rm -rf rootfs
@@ -23,6 +24,12 @@ if [ ! -e rootfs/filesystem_config.txt ] ; then
 	exit 1
 fi
 
+if [ -z "$TOPDIR" ] || [ "$CURDIR" != "$TOPDIR" ] ; then
+	echo "ERROR: You have to execute this script from the ANDROID_BUILD_TOP"
+	echo "ERROR: directory."
+	exit 1
+fi
+
 cp anbox-init.sh rootfs/
 chmod +x rootfs/anbox-init.sh