Neither the `os.Setenv` nor `t.Setenv` helper are safe to use in parallel tests
because environment variables are process-global. The stdlib panics if you try
to do this. Remove the `ci.Parallel()` call from all tests where we're setting
environment variables.
This PR is the first of several for cleaning up warnings, and refactoring
bits of code in the command package. First pass is over acl_ files and
gets some helpers in place.
