Start memcached before installing keystone

Should resolve these errors in dmesg:
    init: keystone main process (32007) terminated with status 1
    init: keystone main process ended, respawning
    init: keystone main process (32012) terminated with status 1
    init: keystone main process ended, respawning
Reorder memcached role so it is just before horizon and controller
Merge pull request #154 from blueboxgroup/memcache-before-keystone

Start memcached before installing keystone