Fix backend line syntax

Fix backend line syntax

Currently since only one node was the backend until this commit[1],
servername was deducted from the $::hostname fact. Since commit[1],
several node can be the backend for a service, so we need to provide
their servername also.

The current situation result with HAProxy refusing to start because
current lint look like

server  192.0.2.2:8776 check fall 5 inter 2000 rise 2

when they really should look like

server MYHOSTNAME  192.0.2.2:8776 check fall 5 inter 2000 rise 2

Resulting in error message : 'server' expects <name> and <addr>[:<port>]
as arguments.

[1] https://review.openstack.org/#/c/168044/

Change-Id: I75424cf02f2d24308f33105f67d82a8d411e372d