<!--- Verify first that your issue is not already reported on GitHub -->
<!--- Also test if the latest release and devel branch are affected too -->
<!--- Complete *all* sections as described, this form is processed automatically -->

##### SUMMARY
<!--- Explain the problem briefly below -->
When looping `include_tasks`, the loop control `loop_var` property is not defined in the included task, when the `loop_var` property has been assigned with a template.

##### ISSUE TYPE
- Bug Report

##### COMPONENT NAME
<!--- Write the short name of the module, plugin, task or feature below, use your best guess if unsure -->
- loop_var
- include_tasks

##### ANSIBLE VERSION
<!--- Paste verbatim output from "ansible --version" between quotes -->
```paste below
ansible 2.8.1
  config file = /playbooks/ansible.cfg
  configured module search path = ['/root/.ansible/plugins/modules', '/usr/share/ansible/plugins/modules']
  ansible python module location = /usr/local/lib/python3.7/site-packages/ansible
  executable location = /usr/local/bin/ansible
  python version = 3.7.3 (default, Jun 11 2019, 01:05:09) [GCC 6.3.0 20170516]
```

##### OS / ENVIRONMENT
<!--- Provide all relevant information below, e.g. target OS versions, network device firmware, etc. -->
Redhat7
Archlinux


##### STEPS TO REPRODUCE
<!--- Describe exactly how to reproduce the problem, using a minimal test-case -->

<!--- Paste example playbooks or commands between quotes below -->
```yaml
---
# main.yml
- hosts: localhost
  vars:
    loop_var_name: custom_var

  tasks:
    - include_tasks: looped-include.yml
      loop:
        - first
        - second
      loop_control:
        loop_var: "{{ loop_var_name }}"
```

```yaml
---
# looped-include.yml
- name: Print looped var
  debug:
    var: custom_var

- name: Loop default item var
  debug:
    var: item
```

<!--- HINT: You can paste gist.github.com links for larger files -->

##### EXPECTED RESULTS
<!--- Describe what you expected to happen when running the steps above -->
We expect the variabe `custom_var` to be the looped variable, and `item` to be undefined. 

##### ACTUAL RESULTS
<!--- Describe what actually happened. If possible run with extra verbosity (-vvvv) -->
Neither `custom_var` nor `item` are defined in the looped included task.

<!--- Paste verbatim command output between quotes -->
```paste below
PLAY [localhost] *****************************************************************************************

TASK [Gathering Facts] ***********************************************************************************
ok: [localhost]
included: /ansible-bug/looped-include.yml for localhost
included: /ansible-bug/looped-include.yml for localhost

TASK [Print looped var] **********************************************************************************
ok: [localhost] => 
  custom_var: VARIABLE IS NOT DEFINED!

TASK [Loop default item var] *****************************************************************************
ok: [localhost] => 
  item: VARIABLE IS NOT DEFINED!

TASK [Print looped var] **********************************************************************************
ok: [localhost] => 
  custom_var: VARIABLE IS NOT DEFINED!

TASK [Loop default item var] *****************************************************************************
ok: [localhost] => 
  item: VARIABLE IS NOT DEFINED!
```

for include_result in include_results:
                    
                    if 'skipped' in include_result and include_result['skipped'] or 'failed' in include_result and include_result['failed']:
                        continue
                    cache_key = (iterator._play, original_host, original_task)
                    try:
                        task_vars = task_vars_cache[cache_key]
                    except KeyError:
                        task_vars = task_vars_cache[cache_key] = variable_manager.get_vars(play=iterator._play, host=original_host, task=original_task)
                    include_args = include_result.get('include_args', dict())
                    special_vars = {}
                    loop_var = 'item'
                    index_var = None
                    if original_task.loop_control:
                        loop_var = original_task.loop_control.loop_var
                        index_var = original_task.loop_control.index_var
                    if loop_var in include_result:
                        task_vars[loop_var] = special_vars[loop_var] = include_result[loop_var]
                    if index_var and index_var in include_result:
                        task_vars[index_var] = special_vars[index_var] = include_result[index_var]
                    if '_ansible_item_label' in include_result:
                        task_vars['_ansible_item_label'] = special_vars['_ansible_item_label'] = include_result['_ansible_item_label']
                    if original_task.no_log and '_ansible_no_log' not in include_args:
                        task_vars['_ansible_no_log'] = special_vars['_ansible_no_log'] = original_task.no_log
                    
                    
                    task_vars['ansible_search_path'] = original_task.get_search_path()
                    
                    if loader.get_basedir() not in task_vars['ansible_search_path']:
                        task_vars['ansible_search_path'].append(loader.get_basedir())