fix bogus dhcpd config

- move failover peer declaration to beginning of file
- set split only on primary
- fix re2o-service hostname
- add /etc/default/isc-dhcp-server

network.yml

@@ -22,7 +22,7 @@
     service_name: dhcp
     service_version: master
     service_config:
-      hostname: re2o.adm.auro.re
+      hostname: re2o.auro.re
       username: service-user
       password: "{{ vault_serviceuser_passwd }}"
   roles: