Fix $TEST_ENV_NUMBER replacing code to not affect all processes

[kiskoza]

Hi. I was trying to create a small script running some custom tests in parallel where I need the TEST_ENV_NUMBER in an other ENV variable, so I naturally tried to reassing it, something like this:

parallel_test -n 3 --first-is-1 -e 'bash -c "export CI_NODE_TOTAL=3 && export CI_NODE_INDEX=$TEST_ENV_NUMBER && echo $CI_NODE_INDEX / $CI_NODE_TOTAL"'

However, it printed 1 / 3 for all processes instead of 1 / 3, 2 / 3 and 3 / 3. Then I found this line that replaces $TEST_ENV_NUMBER and ${TEST_ENV_NUMBER} with the current number by modifying the original cmd array which affects all the other processes as there won't be $TEST_ENV_NUMBER substring in them anymore.

I added one spec that initially failed on the branch and got fixed by my change, I hope I found the right place for it.

Let me know if you need anything else :)

Checklist

• Feature branch is up-to-date with master (if not - rebase it).
• Added tests.
• Added an entry to the Changelog if the new
  code introduces user-observable changes.
• Update Readme.md when cli options are changed

[grosser]

awesome bugfix and great test, thx!

you might want to use the actual parallel unix command, which is much more lightweight :)

[grosser]

4.2.1