In docker-puppet.py, we only create docker-puppet.sh script if it
doesn't exist yet. It's not useful to re-create it and it can be
dangerous to regenerate the script while docker-puppet.py is running,
since we bind mount the script to the containers.
It's possible that during a multi-process task, the script changes and
then the entrypoint fails to run correctly if the interpreter is not
present in the script.
This patch makes sure that we create the script only when needed, and
also that we remove it before running docker-puppet.py, which will be
useful when doing clean deployments or upgrades.
Context: https://github.com/containers/libpod/issues/1844
Change-Id: I0ac69adb47f59a9ca82764b5537532014a782913
d8ee4b9e73