Renames old $devstack_dir to $TOP_DIR

This patch renames $devstack_dir which is no longer defined
to $TOP_DIR. Fixes problem where initialisation of ec2 images
for tempest testing was failing.

Change-Id: Ie0cd43209e58c903b1fe6cc528a4971896e6fab1
diff --git a/lib/tempest b/lib/tempest
index 4d91d90..c163a0d 100644
--- a/lib/tempest
+++ b/lib/tempest
@@ -304,7 +304,7 @@
        echo "Prepare aki/ari/ami Images"
        ( #new namespace
            # tenant:demo ; user: demo
-           source $devstack_dir/accrc/demo/demo
+           source $TOP_DIR/accrc/demo/demo
            euca-bundle-image -i "$kernel" --kernel true -d "$BOTO_MATERIALS_PATH"
            euca-bundle-image -i "$ramdisk" --ramdisk true -d "$BOTO_MATERIALS_PATH"
            euca-bundle-image -i "$disk_image" -d "$BOTO_MATERIALS_PATH"