playbook: Use correctly roles/vars

The previous usage lead to impossilibity of overriding variables defined
in role, because they were included forcibly in the tasks for
standalone-shared.

By using default Ansible apporach to role vars, they can be overriden on
playbook basis.

playbook/roles/standalone-shared/tasks/main.yml

 ---
   - include: debian9-gcc-4.9.yml
 
-  - name: fetch shared vars
-    include_vars: erp5-common.yml
-
   - name: Store public IPv4 for other scripts
     copy: content="{{ ansible_default_ipv4.address }}" dest=/tmp/playbook-public-ipv4 mode=0644
 

playbook/roles/standalone-shared/vars/erp5-common.yml → playbook/roles/standalone-shared/vars/main.yml

@@ -5,4 +5,4 @@ firewall_setup_template: setup-firewall.j2
 frontend_master_reference: master-frn-{{ playbook_name }}
 frontend_slave_reference: slave-srn-{{ playbook_name }}
 backend_url_path: /tmp/playbook-{{ playbook_name }}-backend-url
-public_ipv4_path: /tmp/playbook-{{ playbook_name }}-public_ipv4
+public_ipv4_path: /tmp/playbook-{{ playbook_name }}-public_ipv4
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