split network plugins into distinct roles

roles/network_plugin/flannel/defaults/main.yml

@@ -0,0 +1,8 @@
+---
+# Flannel public IP
+# The address that flannel should advertise as how to access the system
+flannel_public_ip: "{{ access_ip|default(ip|default(ansible_default_ipv4.address)) }}"
+
+## interface that should be used for flannel operations
+## This is actually an inventory node-level item
+# flannel_interface: