In 6418587837 we removed the extra vars from
several roles. Well it's actually important in just one, and only sometimes.
Anyways if and only if the dns server gets set incorrectly on nodes (happens
when the lab is having trouble) collectd adds a DNS server, 8.8.8.8 by default
which means we go from "it might work eventually" to "guaranteed to never work"
once CollectD runs without the dns_server var changed from default.
This went unnoticed because days can pass between issues like this. Anyways
alls the builds are failing now on it, so need to readd it at least here.
Change-Id: I5a32562e19415d29764c9b22aec95fa3dc95ad85
b171ccbe07