better handling of pip-as-root warnings

Author: minchinweb

Dockerfile

@@ -46,16 +46,18 @@ RUN \
     rm -rf /var/lib/apt/lists/*
 
 # disable checks for `pip` upgrades (we're upgrading anyway)
-ENV PIP_DISABLE_PIP_VERSION_CHECK=1
+ARG PIP_DISABLE_PIP_VERSION_CHECK=1
 # don't write .pyc files
 # https://stackoverflow.com/questions/59732335/is-there-any-disadvantage-in-using-pythondontwritebytecode-in-docker
 ENV PYTHONDONTWRITEBYTECODE=1
 # ensures console output is not buffered by Docker
 ENV PYTHONUNBUFFERED=1
+# Ignore warnings about running pip as root, but only for the build
+ARG PIP_ROOT_USER_ACTION=ignore
 
 RUN python -m pip --version
-RUN python -m pip install pip --upgrade --root-user-action
-RUN python -m pip install setuptools wheel build --upgrade --root-user-action
+RUN python -m pip install pip --upgrade
+RUN python -m pip install setuptools wheel build --upgrade
 
 # store Python Version; used for image tagging
 # ARG needs to be declared here, and above any FROM line