fixed issues with coverage and pylint results

Fixed a few problems in the coverage and pylint results.

- The file paths were incorrect so Jenkins was not able to find files for per-file highlighted view.
- Reports included files that don't belong to nltk.

After this fix is in place, old coverage and pylint files in the nltk/test directory need to be removed from workspaces on the ShinngPanda executor vm, which I can do.