ubuntu: add df_dev env

base-ubuntu/Dockerfile

@@ -3,7 +3,9 @@ FROM ubuntu:${VARIANT}
 RUN userdel -r ubuntu || echo "User ubuntu does not exist, continuing..."
 
 ENV TERM=xterm-256color
-ENV DEBIAN_FRONTEND=noninteractive
+ENV DF_DEV=true
+
+ARG DEBIAN_FRONTEND=noninteractive
 
 RUN apt-get update && apt-get upgrade -y && apt-get install -y --no-install-recommends \
   # basics