Add an enhanced debug configuration technique to caching guide
Add an enhanced debug configuration technique to caching guide

We often have operators ask why cache logging isn't included in their
logs despite setting `keystone.conf [DEFAULT] debug=True`. This is
because cache logging requires additional configuration that isn't
obvious unless your familiar with oslo.cache and dogpile already.

This commit adds a section to the caching guide that shows people how to
update their configuration files when they need to debug caching issues.

Change-Id: I33d37366ea9caf320f3738db637dea7386ff6448

openstack/keystone,mahak/keystone,openstack/keystone,mahak/keystone,mahak/keystone,openstack/keystone