##### 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]
```

'''
        Helper function to add a new host to inventory based on a task result.
        '''
        if host_info:
            host_name = host_info.get('host_name')
            
            if host_name not in self._inventory.hosts:
                self._inventory.add_host(host_name, 'all')
                self._hosts_cache_all.append(host_name)
            new_host = self._inventory.hosts.get(host_name)
            
            new_host.vars = combine_vars(new_host.get_vars(), host_info.get('host_vars', dict()))
            new_groups = host_info.get('groups', [])
            for group_name in new_groups:
                if group_name not in self._inventory.groups:
                    group_name = self._inventory.add_group(group_name)
                new_group = self._inventory.groups[group_name]
                new_group.add_host(self._inventory.hosts[host_name])
            
            self._inventory.reconcile_inventory()
    def _add_group(self, host, result_item):