Make spof.pp able to live with loadbalancer.pp

In some cases as described in #237, `spof.pp` and `loadbalancer.pp`
might be instantiated on the same server. Thus, we need to make
sure the instantiation of corosync and pacemaker core components
do not result in a duplicate error.

Related #237
Make loadbalancer.pp fit active/active or active/passive configuration

This commit allows one to specify if the loadbalancer is deployed
using haproxy/keepalived or haproxy/pacemaker, specifying the
`$active_active` value. In one case HAProxy binds on `0.0.0.0`
on the other it binds on the various vips (public, internal).

Related #237
Renamed $api_eth to $internal_netif_if to match params.pp

The name of the $api_eth is unclear and do not reflect what
is the actual variable.

Related #237
Change httpchk options for horizon

In order to have clean log in apache, we need to do
a GET call instead of the default OPTIONS call. Also we
specify a User Agent, for better filtering.

Related to #237
Implement sticky/persistent session with HAProxy

This commit implements sticky/persisten session between
HAProxy and Horizon based on the leastconn fashion

Related to #237