common: Add a maintenance_remote_machine variable

Add a variable that takes the SSH_CLIENT environment variable to save the
ip address of the machine actually running the playbooks. This can be used
on maintenance mode to allow in the person running the playbook and let
everybody else to see the maintenance page.

group_vars/all/common.yml

@@ -6,3 +6,7 @@ ansible_python_interpreter: /usr/bin/python3
 
 zabbix_agent_templates:
   - Template OS Linux
+
+# this is used by the maintenance role to get the ip address
+# of the machine running the playbook
+maintenance_remote_machine: "{{ hostvars[inventory_hostname]['ansible_env'].SSH_CLIENT.split(' ')[0] }}"