##### 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]
```

handler=task,
                                handler_name=task_name,
                                iterator=iterator,
                                play_context=play_context,
                                notified_hosts=included_file._hosts[:],
                            )
                            if not result:
                                break
                except AnsibleError as e:
                    for host in included_file._hosts:
                        iterator.mark_host_failed(host)
                        self._tqm._failed_hosts[host.name] = True
                    display.warning(to_text(e))
                    continue
        
        handler.notified_hosts = [
            h for h in handler.notified_hosts
            if h not in notified_hosts]
        display.debug("done running handlers, result is: %s" % result)
        return result
    def _filter_notified_failed_hosts(self, iterator, notified_hosts):
        return []
    def _filter_notified_hosts(self, notified_hosts):
        '''
        Filter notified hosts accordingly to strategy
        '''
        
        
        return notified_hosts[:]
    def _take_step(self, task, host=None):