Enable caching
Enable caching

memcached should be enabled in os_keystone by default, but it's not, so
we have to pass an extra variable to the playbook.

For referenced, this is also fixed upstream here:

    https://review.openstack.org/#/c/326748/

Issue #14

lbragstad/keystone-performance,lbragstad/keystone-performance,lbragstad/keystone-performance