hosts: hass1: Set collectd network interface

Because *hass1.pyrocufflink.blue* has multiple interfaces, collectd does
not know which interface it should use to send multicast metrics
messages.  To force it to use the wired interface, which is connected to
the default internal ("blue") network, the `interface` property needs to
be set.

host_vars/hass1.pyrocufflink.blue.yml

@@ -1,2 +1,5 @@
 burp_backup:
 - include: /var/lib/homeassistant
+collectd_network_servers:
+- host: ff18::efc0:4a42
+  interface: eth0