(ansible) A less complicated hosts mapping

[mieel]

Description of feature

Stackl should be able to pass a list of hostnames to an ansible invocation without using a stackl inventory or policies.
Configuration should be minimal like this:

# postgres-service.yml
  name: postgres-service
  functional_requirements:
    azure_vm: # creates 2 database servers, 3 frontend webservers
      params:
        vm_count: 2
        vm_size: large
    postgres_role:
      params:
        ansible_hosts: "{{ azure_vm.outputs.vm_private_ips }}"
        # postgres_role is going to apply the role on all hosts in the above list

# frontend-service.yml
  name: frontend-service
  functional_requirements:
    azure_vm: # creates 2 database servers, 3 frontend webservers
      params:
        vm_countL: 3
        vm_size: small
    webserver_role:
      params:
        ansible_hosts: "{{ azure_vm.outputs.vm_private_ips }}"
        # webserver_role is going to apply the role on all hosts in the above list

Purpose of this new feature

Defining stackl inventory params is cumbersome and very limited.
Passing a list from the provisioning step is much more intuitive, and less error prone.

[mieel]

partially solved by #250