##### 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]
```

"""Continue to next result"""
        self.next_action.result = NextAction.CONTINUE
        return True
    do_c = do_continue
    def do_redo(self, args):
        """Schedule task for re-execution. The re-execution may not be the next result"""
        self.next_action.result = NextAction.REDO
        return True
    do_r = do_redo
    def do_update_task(self, args):
        """Recreate the task from ``task._ds``, and template with updated ``task_vars``"""
        templar = Templar(None, shared_loader_obj=None, variables=self.scope['task_vars'])
        task = self.scope['task']
        task = task.load_data(task._ds)
        task.post_validate(templar)
        self.scope['task'] = task
    do_u = do_update_task
    def evaluate(self, args):
        try:
            return eval(args, globals(), self.scope)
        except Exception:
            t, v = sys.exc_info()[:2]
            if isinstance(t, str):
                exc_type_name = t
            else:
                exc_type_name = t.__name__
            display.display('***%s:%s' % (exc_type_name, repr(v)))
            raise
    def do_pprint(self, args):