Decouple etcd defaults in a separate role

This allows us to reuse the defaults in other places without putting
everything in kubespray-defaults.

In that, for kubernetes/control-plane.

roles/etcd/meta/main.yml

@@ -6,3 +6,4 @@ dependencies:
   - role: adduser
     user: "{{ addusers.kube }}"
     when: not (ansible_os_family in ["Flatcar", "Flatcar Container Linux by Kinvolk", "ClearLinux"] or is_fedora_coreos)
+  - role: etcd_defaults