245 support the new version of khiops env

[popescu-v]

All minor stuff.

However, it doesn't work in macOS. A change in khiops_env is necessary.

Update:

I'd also make private get_linux_distribution_name , check_samples_dir and get_dir_status so they dont pollute the documentation.

• get_linux_distribution_name was moved to test_khiops_integrations.py and made private therein; it is no longer necessary in the runner code (as those variables are set by khiops_env now).
• the two other methods were made private.