Dockerfile lint errors fix (#1493)

Fix the Dockerfile linter errors and most warnings

test-tools/IoT-APP-Store-Demo/wasm_django/Dockerfile

@@ -1,9 +1,9 @@
 FROM python:3.5
 
 WORKDIR /app
-ADD . /app
+COPY . /app
 
-RUN pip install django
+RUN pip install django --no-cache-dir
 
 ENTRYPOINT ["python", "manage.py", "runserver", "0.0.0.0:80"]