##### SUMMARY
I'll start by saying that this is a bit of a weird one. It seems that when a handler task is included from another handler and notifies yet another handler, ansible generates spurious warnings and then hangs.

Just to confuse things even more, if you remove the variable reference in `name` OR the `notify` from `bar_handler_tasks.yml`, ansible executes normally.

Another thing to note is that this code (or something very much like it) apparently worked properly in Ansible 2.7.

##### ISSUE TYPE
- Bug Report

##### COMPONENT NAME
handlers

##### ANSIBLE VERSION
```
ansible 2.8.1
  config file = /etc/ansible/ansible.cfg
  configured module search path = [u'/home/agaffney/.ansible/plugins/modules', u'/usr/share/ansible/plugins/modules']
  ansible python module location = /usr/lib/python2.7/dist-packages/ansible
  executable location = /usr/bin/ansible
  python version = 2.7.12 (default, Nov 12 2018, 14:36:49) [GCC 5.4.0 20160609]
```

##### CONFIGURATION
N/A

##### OS / ENVIRONMENT
N/A

##### STEPS TO REPRODUCE

`bar.yml`:

```yaml
- hosts: localhost
  gather_facts: no
  handlers:
    - name: play handler 1
      include_tasks: bar_handler_tasks.yml

    - name: play handler 2
      debug:
        msg: play handler 2

  tasks:
    - name: trigger handler 1
      debug:
        msg: trigger handler 1
      changed_when: true
      notify: play handler 1
```

`bar_handler_tasks.yml`:

```yaml
- name: included handler 1 {{ inventory_hostname }}
  debug:
    msg: included handler 1

- name: included handler 2
  debug:
    msg: whatever
  changed_when: true
  notify: play handler 2
```

##### EXPECTED RESULTS
<!--- Describe what you expected to happen when running the steps above -->


##### ACTUAL RESULTS
```
PLAY [localhost] **************************************************************************************************************************************************************************************************************************************************************

TASK [trigger handler 1] ******************************************************************************************************************************************************************************************************************************************************
changed: [localhost] => {
    "msg": "trigger handler 1"
}

RUNNING HANDLER [play handler 1] **********************************************************************************************************************************************************************************************************************************************
included: /tmp/ansible_test/kiwiirc/bar_handler_tasks.yml for localhost

RUNNING HANDLER [included handler 1 {{ inventory_hostname }}] *****************************************************************************************************************************************************************************************************************
ok: [localhost] => {
    "msg": "included handler 1"
}

RUNNING HANDLER [included handler 2] ******************************************************************************************************************************************************************************************************************************************
 [WARNING]: 'inventory_hostname' is undefined

RUNNING HANDLER [included handler 2] ******************************************************************************************************************************************************************************************************************************************
 [ERROR]: User interrupted execution
```

import os
import pprint
import sys
import threading
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.helpers import load_list_of_blocks
from ansible.playbook.included_file import IncludedFile
from ansible.playbook.task_include import TaskInclude
from ansible.plugins.loader import action_loader, connection_loader, filter_loader, lookup_loader, module_loader, test_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']
class StrategySentinel: