Adds Memcached Support

Previously, nova could only use the in-process cache
to store information such as console-auth tokens.

This change allows nova to use memcached as a
backend to store information.

Defaults to false for backwards compatability and allow
nova to continue using the in-process cache.

Change-Id: If05f04127bc1ec849bec9fd74b2d8027108635e4
Merge "Adds Memcached Support"