haproxy stats socket level user 666

HAProxy 1.5 allows mulitple stats sockets with different levels, but
Trusty only has v1.4. For now, run the 'user' level socket for the
Icinga checks rather than over exposing 'admin' level (which would be
most useful for other stuff, like, say, admin-ing...). For the simple
use case of primary/secondary failover this isn't a show stopper.

Change-Id: I13ee4aa02faca8f76e3395bcbfd8dd7aa9a696c6