##### SUMMARY
add_host will return 'changed' for every invocation, it does not matter if the host already existed and no changes were actually made to inventory

##### ISSUE TYPE
- Bug Report

##### COMPONENT NAME
<!--- Write the short name of the module, plugin, task or feature below, use your best guess if unsure -->
add_host
##### ANSIBLE VERSION
<!--- Paste verbatim output from "ansible --version" between quotes -->
```paste below
2.7, 2.8, 2.9, 2.10
```

##### CONFIGURATION
<!--- Paste verbatim output from "ansible-config dump --only-changed" between quotes -->
```paste below

```

##### OS / ENVIRONMENT
<!--- Provide all relevant information below, e.g. target OS versions, network device firmware, etc. -->
all

##### STEPS TO REPRODUCE

Simplest example, but also happens when specifying variables and/or groups

test.yml
```yaml
- hosts: localhost
  gather_facts: false
  tasks:
    - add_host: name=testhost
```
test_inv.ini
```ini
testhost
```
run:
``` ansible-playbook -i test_inv.ini test.yml```

<!--- HINT: You can paste gist.github.com links for larger files -->

##### EXPECTED RESULTS
<!--- Describe what you expected to happen when running the steps above -->
```
 _________________
< TASK [add_host] >
 -----------------
       \   ,__,
        \  (oo)____
           (__)    )\
              ||--|| *

OK: [localhost]
```

##### ACTUAL RESULTS
<!--- Describe what actually happened. If possible run with extra verbosity (-vvvv) -->

<!--- Paste verbatim command output between quotes -->
```paste below
 _________________
< TASK [add_host] >
 -----------------
       \   ,__,
        \  (oo)____
           (__)    )\
              ||--|| *

changed: [localhost]
```

if not found:
                                    msg = ("The requested handler '%s' was not found in either the main handlers list nor in the listening "
                                           "handlers list" % handler_name)
                                    if C.ERROR_ON_MISSING_HANDLER:
                                        raise AnsibleError(msg)
                                    else:
                                        display.warning(msg)
                    if 'add_host' in result_item:
                        
                        new_host_info = result_item.get('add_host', dict())
                        self._add_host(new_host_info, iterator)
                    elif 'add_group' in result_item:
                        
                        self._add_group(original_host, result_item)
                    if 'ansible_facts' in result_item:
                        
                        if original_task.delegate_to is not None and original_task.delegate_facts:
                            host_list = self.get_delegated_hosts(result_item, original_task)
                        else:
                            
                            self._set_always_delegated_facts(result_item, original_task)
                            host_list = self.get_task_hosts(iterator, original_host, original_task)
                        if original_task.action == 'include_vars':
                            for (var_name, var_value) in iteritems(result_item['ansible_facts']):
                                
                                
                                for target_host in host_list:
                                    self._variable_manager.set_host_variable(target_host, var_name, var_value)
                        else:
                            cacheable = result_item.pop('_ansible_facts_cacheable', False)