Multiple group for host

[c-dst]

Hi,
Same way as #32, my host is in multiple group with different rules to merge but I dont want to turn on the global merge config option.

I updated the template in this way to solve my need :
{% set _ = merged.update(firewall_v4_group_rules) %}
{% for group in group_names %}
{% set _ = merged.update( lookup('vars', 'firewall_v4_group_' + group + '_rules', default="" ) ) %}
{% endfor %}

Lookup on the host group an merge var like firewall_v4_group__rules or and empty string if not defined. The "firewall_v4_group_rules stay in place to keep initial feature.