##### 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]
```

self._tqm.send_callback('v2_runner_on_ok', task_result)
            
            if original_task.register:
                host_list = self.get_task_hosts(iterator, original_host, original_task)
                clean_copy = strip_internal_keys(module_response_deepcopy(task_result._result))
                if 'invocation' in clean_copy:
                    del clean_copy['invocation']
                for target_host in host_list:
                    self._variable_manager.set_nonpersistent_facts(target_host, {original_task.register: clean_copy})
            if do_handlers:
                self._pending_handler_results -= 1
            else:
                self._pending_results -= 1
            if original_host.name in self._blocked_hosts:
                del self._blocked_hosts[original_host.name]
            
            
            if original_task._role is not None and role_ran:  
                
                
                for (entry, role_obj) in iteritems(iterator._play.ROLE_CACHE[original_task._role.get_name()]):
                    if role_obj._uuid == original_task._role._uuid:
                        role_obj._had_task_run[original_host.name] = True
            ret_results.append(task_result)
            if one_pass or max_passes is not None and (cur_pass + 1) >= max_passes:
                break
            cur_pass += 1
        return ret_results
    def _wait_on_handler_results(self, iterator, handler, notified_hosts):