use get_container_info in ratelimit

Everyone else cooperates to store the container_info cache in the env the
first time it's requested.  This should save a duplicate memcache hit on
requests that ratelimiting looks at.

Change-Id: Ic6411d4619db6b53fafe9fdbf1d0a370d1258c38
Merge "use get_container_info in ratelimit"