loadbalancer.pp: Enable HAProxy binding on 80 and 443

Currently, one can enable HA only on plain http or https
for horizon, but can't have it enabled for both at the
same time.

This commit makes configuration for horizon http and https
completly independent, one can decide to enable one and not
the other, add specific bind options for one and not the
other, etc...
Merge pull request #598 from enovance/haproxy_horizon_allow_ssl_and_80

loadbalancer.pp: Enable HAProxy binding on 80 and 443