Avoid temporary service outage with error 503

When horizon is deploed in a HA setup, haproxy is used. In every chef run, the
ports the apache server is listening to are first set to the default values,
and in a later cookbook to the haproxy values. When checking from the beginning
if the haproxy values are needed, we avoid unnecessary changes to the config
file causing apache2 restarts that result in a temporary service outage with
error 503.

See also https://bugzilla.novell.com/show_bug.cgi?id=897996
So really, I think the question is: why is this file written several times on a chef run, and sometimes with not the ports we expect?