### Summary

Executing a playbook with many hosts, there is massive overhead in checking whether the hosts list is a pattern, see for yourself on this callgrind graph:

![grafik](https://user-images.githubusercontent.com/3154871/111359016-4a4bf480-868b-11eb-8c8f-55b6a6a10bd7.png)

https://github.com/ansible/ansible/blob/da60525610a384bb04833b1c6429d9db6a87ef64/lib/ansible/vars/manager.py#L490

That check has quadratic runtime with the number of hosts - with a lot of hosts, commenting that check out reduces runtime manyfold.

### Issue Type

Bug Report

### Component Name

variable manager

### Ansible Version

2.10.5, devel

### OS / Environment

Ubuntu

### Steps to Reproduce

```yaml
- hosts: localhost
  tasks:
    - set_fact:
        extra_tasks: true # compute it
        hosts: "{{ [an, array, with, 5100, computed, hosts] }}"

- hosts: "{{ hostvars.localhost.hosts }}"
  vars:
    extra_tasks: "{{ hostvars.localhost.do_extra_tasks }}"
  tasks:
   # some more tasks here
    - name: Execute extra tasks
      command: /bin/true # example
      when: extra_tasks
```

### Expected Results

Execute in tens of seconds.

### Actual Results

Take over 5 minutes to execute.
state, _ = iterator.get_next_task_for_host(h, peek=True)
                                iterator.mark_host_failed(h)
                                state, new_task = iterator.get_next_task_for_host(h, peek=True)
                    else:
                        iterator.mark_host_failed(original_host)
                    
                    
                    
                    state, _ = iterator.get_next_task_for_host(original_host, peek=True)
                    if iterator.is_failed(original_host) and state and state.run_state == iterator.ITERATING_COMPLETE:
                        self._tqm._failed_hosts[original_host.name] = True
                    
                    
                    
                    
                    if state and (iterator.get_active_state(state).run_state == iterator.ITERATING_RESCUE or
                                  iterator.is_any_block_rescuing(state)):
                        self._tqm._stats.increment('rescued', original_host.name)
                        self._variable_manager.set_nonpersistent_facts(
                            original_host.name,
                            dict(
                                ansible_failed_task=wrap_var(original_task.serialize()),
                                ansible_failed_result=task_result._result,
                            ),
                        )
                    else:
                        self._tqm._stats.increment('failures', original_host.name)
                else:
                    self._tqm._stats.increment('ok', original_host.name)
                    self._tqm._stats.increment('ignored', original_host.name)