simplify the Dockerfiles

[Jirka Borovec]

simplify the docker files by using an input parameter for versions of python and/or openCV

https://vsupalov.com/docker-arg-env-variable-guide

for building with the parameter you just need to do in the Dockerfile to make the
ARG some_variable_name line and then release build docker build --build-arg some_variable_name = a_value