[bugfix] Test all packages with l10n_tests.py
[bugfix] Test all packages with l10n_tests.py

- add package parameter to test_method all packages
- use i18n.twhas_key to verify that a translation message exists;
  otherwise a TranslationError will be raised
- skip tests on some sites where these aren't applicable

Bug: T225631
Bug: T225781
Change-Id: I13ec0f1761db95a50c1a871659fdea52cc3ce2d0

wikimedia/pywikibot-core,wikimedia/pywikibot-core,PersianWikipedia/pywikibot-core