Update sessions and cache to memcached

Summary:
Session cache config

update variables from config

fix core

ruby error

proper cake and memcache

Test Plan: working on stage

Reviewers: #everyone

Differential Revision: https://dev.blendtec.com/D1517
prefix the cache prefix with hostname

Summary: prefix the cache prefix with hostname

Test Plan: already working on stage

Reviewers: #everyone, gwarner

Reviewed By: #everyone, gwarner

Differential Revision: https://dev.blendtec.com/D1519
Update core to actually handle sessions correctly

Summary: Allows for core to be different but share the rest

Test Plan: None

Reviewers: #everyone, jslemboski

Reviewed By: #everyone, jslemboski

Subscribers: mclawson

Differential Revision: https://dev.blendtec.com/D1564