Add additional BuildRequires for i18n locales used in tests
    
    The test suite uses is_IS.UTF-8 and is_IS.ISO8859-1 (via the
    GETTEXT_LOCALE and GETTEXT_ISO_LOCALE prereq's.  Ensure these locales
    are available.  Installing glibc-langpack-is is insufficient as it does
    not provide is_IS.ISO8859-1, glibc-all-langpacks is also needed.
    
    Now that we're installing additional langpacks, update the macro name
    which was added in a6a24cf ("Add glibc-langpack-en BuildRequires for
    en_US.UTF-8 locale", 2018-11-05).