This change makes the Meta/import-wpt-test.py script handle URLs such as
https://wpt.live//WebCryptoAPI/generateKey/../util/helpers.js and paths
containing, e.g., wpt-import/WebCryptoAPI/generateKey/../util/helpers.js
(that is, URLs and paths with “..” parent-directory references in them).
Otherwise, without this change, when the import-wpt-test.py script tries
a URL like https://wpt.live//WebCryptoAPI/generateKey/../util/helpers.js
which contains a “..” parent-directory reference, the script fails with
a “urllib.error.HTTPError: HTTP Error 404: Not Found” error message.
