[lint] Add attr to import whitelist
[lint] Add attr to import whitelist

The attr module cannot touch external state and is used widely
throughout recipes, so it makes sense to add it to this whitelist. The
only reason this hasn't caused an issue before now is that attr is
mostly used by recipe modules, and `recipes.py lint` doesn't support
validation of recipe module imports yet.

I also renamed some variables to avoid "whitelist", for the purposes of
inclusivity. I didn't change anything user-facing like argument names or
help strings.

Change-Id: I860cad13c3960fb74a8745fafc8c11d0ed25be97
Reviewed-on: https://chromium-review.googlesource.com/c/infra/luci/recipes-py/+/2261077
Commit-Queue: Oliver Newman <c98d05fdc4005e0f75e160701d6b971b76237a97@google.com>
Reviewed-by: Robbie Iannucci <40f3d43a28ebae3cb819288542e1c84d73d962d5@chromium.org>

luci/recipes-py,luci/recipes-py