MEMOIZE_TOKENS set token to cache when validating token

[jun923.gu]

We encounter this situation that MEMOIZE_TOKENS decorator will set token to cache when validating token. We take a deeper look at the cache codes and found that dogpile will call get_or_create function. That is, if fail to get token from cache, dogpile will set token to cache. As we config CONF.token.cache_on_issue to False, we would not wish token setted into cache.