Add cpu_mode in quickstart guide
Add cpu_mode in quickstart guide

With libvirt 2.0, when using qemu cpu mode is not properly
evaluated and need to be set to cpu_mode = none.

Add this option when kvm is not supported, otherwise user
will still facing errors when launching instances over qemu.

Change-Id: Ic970e3de74817ce4e17bb4e15d130e1e82d595cc

dardelean/kolla-ansible,dardelean/kolla-ansible,dardelean/kolla-ansible