Comment 0 for bug 1582585

In our project,we found that the speed of query user from ldap server was very slow(our ldap user number is 12,000,the query costs almost 45 seconds)

The reason is that keystone will generate the uuid for the ldap users one by one and insert db.
And second time query,it also goes to db,not use the cache to improve the speed.

So we can add the cache to improve the query speed
After add @MEMOIZE to the following function
https://github.com/openstack/keystone/blob/master/keystone/identity/core.py#L580,
the query costs 7 seconds,but first query almost costs 50 seconds