test: make test-intl-no-icu-data more robust

In V8 5.6, String#toLocaleUpperCase can work even when no ICU data is
loaded. Use another method to check the --icu-data-dir option pointing
to an empty directory.

PR-URL: https://github.com/nodejs/node/pull/10992


Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>