Ensure cleanup executes for scripts-whitespace-windows test.

Test failure was leaving an assortment of files dangling around:
   test/tap/scripts-whitespace-windows/cache/scripts-whitespace-windows-dep/0.0.1/package.tgz
   test/tap/scripts-whitespace-windows/cache/scripts-whitespace-windows-dep/0.0.1/package/package.json