##### 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]
```

import time
from collections import deque
from multiprocessing import Lock
from jinja2.exceptions import UndefinedError
from ansible import constants as C
from ansible import context
from ansible.errors import AnsibleError, AnsibleFileNotFound, AnsibleParserError, AnsibleUndefinedVariable
from ansible.executor import action_write_locks
from ansible.executor.process.worker import WorkerProcess
from ansible.executor.task_result import TaskResult
from ansible.inventory.host import Host
from ansible.module_utils.six.moves import queue as Queue
from ansible.module_utils.six import iteritems, itervalues, string_types
from ansible.module_utils._text import to_text
from ansible.module_utils.connection import Connection, ConnectionError
from ansible.playbook.handler import Handler
from ansible.playbook.helpers import load_list_of_blocks
from ansible.playbook.included_file import IncludedFile
from ansible.playbook.task_include import TaskInclude
from ansible.plugins import loader as plugin_loader
from ansible.template import Templar
from ansible.utils.display import Display
from ansible.utils.vars import combine_vars
from ansible.vars.clean import strip_internal_keys, module_response_deepcopy
display = Display()
__all__ = ['StrategyBase']
ALWAYS_DELEGATE_FACT_PREFIXES = frozenset((
    'discovered_interpreter_',
))
class StrategySentinel: