Fix newline issue in reproduce_ci_env.py
MR !2598 introduced some fixes to `reproduce_ci_env.py`. One of them handled newlines in command lists by separating the command lists by newlines in the Dockerfile (which generated a script). Although this worked for some of the docker containers, I found others, like rhel8, where the newlines were not escaped correctly. Correct this problem by moving back to separating commands with `&&`. This requires replacing newlines in commands with `&&`. That in itself is no problem except that if you have a blank line, you get `&& &&`, which is a syntax error for the shell. So, avoid this by stripping newlines from commands.