add with_product for nested loop

I had the need to do nested loop (product): 
```
for x in A:
   for y in B 
     (x,y)
```
i.e: 
Execute a action over a list and delegate_to all host in a group:
```yaml
- name:  My Role | Send configs
  template: src="{{item.0}}" dest=/etc/mysoft/conf.d/ mode=0644
  delegate_to: "{{item.1}}"
  with_product:
    - mytemplates
    - groups['logstash-indexers']
```