Replace hardcoded python version with ARG variable The Dockerfile had a hardcoded Python version in install paths and COPY command in the second stage build. Replace that with a hardcoded ARG pythonversion. Add RUN command to verify pythonversion against the actual version installed in the docker image. If they do not match generate an appropriate --build-arg for the docker build command that will match the docker image version. Document the use of the variable and why it's needed in installation.txt. Also fix typos referencing --build-args and bad values for the arguments.

recursive-include share *
recursive-include roundup *.*
recursive-include frontends *.*
recursive-include scripts *.* *-*
recursive-include scripts/Docker Dockerfile *.* *_*
recursive-include tools *.* base64
recursive-include test *.py *.txt
recursive-include doc *.html *.png *.txt *.css *.example
recursive-include detectors *.py README.txt
global-exclude *.pyc *.pyo .DS_Store *.orig *.rej *~ \#*
include demo.py *.txt
include doc/conf.py doc/roundup-favicon.ico
exclude doc/security.txt
include locale/*.po locale/*.mo locale/roundup.pot