Merge /etc/portage/package.keywords and
    /etc/portage/package.accept_keywords.

def _unify_keywords():
    '''
    Merge /etc/portage/package.keywords and
    /etc/portage/package.accept_keywords.
    '''
    old_path = BASE_PATH.format('keywords')
    if os.path.exists(old_path):
        if os.path.isdir(old_path):
            for triplet in salt.utils.path.os_walk(old_path):
                for file_name in triplet[2]:
                    file_path = '{0}/{1}'.format(triplet[0], file_name)
                    with salt.utils.files.fopen(file_path) as fh_:
                        for line in fh_:
                            line = salt.utils.stringutils.to_unicode(line).strip()
                            if line and not line.startswith('#'):
                                append_to_package_conf(
                                    'accept_keywords', string=line)
            shutil.rmtree(old_path)
        else:
            with salt.utils.files.fopen(old_path) as fh_:
                for line in fh_:
                    line = salt.utils.stringutils.to_unicode(line).strip()
                    if line and not line.startswith('#'):
                        append_to_package_conf('accept_keywords', string=line)
            os.remove(old_path)