Correctly read the cache key for remote cache (#121151)
Summary: While investigating why we were calling put each time, I noticed that memcache backend returns a list instead of direct result, which means that we were correctly fetching the cached result but not using it.
Test Plan: The test should now work as expected
Differential Revision: D54500851
Pull Request resolved: https://github.com/pytorch/pytorch/pull/121151
Approved by: https://github.com/aakhundov
