Env variables interpolation doesn't work inside 'with_items_from_csv'

[RicoGit]

Looks like an interpolation in with_items_from_csv is not worked.

config contains:
with_items_from_csv': /fixtures/{{ RECIPE_IDS_FILE }}
error appeared:
thread 'main' panicked at 'couldn't open /fixtures/{{ RECIPE_IDS_FILE }}: No such file or directory (os error 2)'

Expected:
Unknown 'RECIPE_IDS_FILE' variable! if RECIPE_IDS_FILE is not defined.
Or reading csv file successfully is RECIPE_IDS_FILE is defined.

[fcsonline]

@RicoGit Sorry, but this is not supported right now. You can't have interpolations on these properties. drill reads the benchmark plan file and computes (expands) all the actions / requests to do before running it.

Your interpolation looks like an environment variable. This interpolation could be replaced to be able to open the right file, but the interpolation engine is only available on runtime and would require a huge refactor.

I created a pull request to expose this limitation and handle it better.