##### 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]
```

}
                    worker_prc = WorkerProcess(self._final_q, task_vars, host, task, play_context, self._loader, self._variable_manager, plugin_loader)
                    self._workers[self._cur_worker] = worker_prc
                    self._tqm.send_callback('v2_runner_on_start', host, task)
                    worker_prc.start()
                    display.debug("worker is %d (out of %d available)" % (self._cur_worker + 1, len(self._workers)))
                    queued = True
                self._cur_worker += 1
                if self._cur_worker >= rewind_point:
                    self._cur_worker = 0
                if queued:
                    break
                elif self._cur_worker == starting_worker:
                    time.sleep(0.0001)
            if isinstance(task, Handler):
                self._pending_handler_results += 1
            else:
                self._pending_results += 1
        except (EOFError, IOError, AssertionError) as e:
            
            display.debug("got an error while queuing: %s" % e)
            return
        display.debug("exiting _queue_task() for %s/%s" % (host.name, task.action))
    def get_task_hosts(self, iterator, task_host, task):
        if task.run_once:
            host_list = [host for host in self._hosts_cache if host not in self._tqm._unreachable_hosts]
        else:
            host_list = [task_host.name]
        return host_list
    def get_delegated_hosts(self, result, task):