##### 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]
```

role_ran = True
                ignore_errors = original_task.ignore_errors
                if not ignore_errors:
                    display.debug("marking %s as failed" % original_host.name)
                    if original_task.run_once:
                        
                        for h in self._inventory.get_hosts(iterator._play.hosts):
                            if h.name not in self._tqm._unreachable_hosts:
                                state, _ = iterator.get_next_task_for_host(h, peek=True)
                                iterator.mark_host_failed(h)
                                state, new_task = iterator.get_next_task_for_host(h, peek=True)
                    else:
                        iterator.mark_host_failed(original_host)
                    
                    
                    
                    state, _ = iterator.get_next_task_for_host(original_host, peek=True)
                    if iterator.is_failed(original_host) and state and state.run_state == iterator.ITERATING_COMPLETE:
                        self._tqm._failed_hosts[original_host.name] = True
                    if state and iterator.get_active_state(state).run_state == iterator.ITERATING_RESCUE:
                        self._tqm._stats.increment('rescued', original_host.name)
                        self._variable_manager.set_nonpersistent_facts(
                            original_host.name,
                            dict(
                                ansible_failed_task=original_task.serialize(),
                                ansible_failed_result=task_result._result,
                            ),
                        )
                    else:
                        self._tqm._stats.increment('failures', original_host.name)