### Summary

Within `AnsibleModule.run_command()`, prior to calling `subprocess.Popen`, it uses `os.environ.get()` to read some environment variables:

https://github.com/ansible/ansible/blob/v2.11.0/lib/ansible/module_utils/basic.py#L1947

After the `Popen` call, it deletes some environment variables that were added using `del os.environ[]`:

https://github.com/ansible/ansible/blob/v2.11.0/lib/ansible/module_utils/basic.py#L2091

Unfortunately, this is not thread-safe when Ansible hits Python 2 targets (eg. CentOS 7). The Python 2 standard library implements `.get()` non-atomically:
```python
    def get(self, key, failobj=None):
        if key not in self:
            return failobj
        return self[key]
```

This surfaces in Ansible primarily during the fact collection process in `module_utils/facts/hardware/linux.py`, where several threads in a `multiprocessing.pool.ThreadPool` call `run_process()` to collect block device information. When the race condition is hit, a `KeyError` is raised, breaking the mount point fact gathering and leaving the facts unavailable.

In our environment, when running against 1000+ CentOS 7 hosts, this race condition will be intermittently hit on only 1-2 hosts, making this difficult to troubleshoot. Because it's very hard to reproduce with fewer hosts, I created a script to demonstrate how the `os.environ` mutation is problematic: https://gist.github.com/agunnerson-ibm/b7a956d05095c5fad885295e2e31c9a4

Is it possible to refactor `run_command()` so that it makes a copy of `os.environ`, mutates the copy, and then passes it to `subprocess.Popen` via the `env=` kwarg? I believe that would fix this race condition and would remove the current implementation's need to back up and restore environment variables.

### Issue Type

Bug Report

### Component Name

module_utils/basic

### Ansible Version

```console
ansible [core 2.11.0]
  config file = None
  configured module search path = ['/home/jenkins/.ansible/plugins/modules', '/usr/share/ansible/plugins/modules']
  ansible python module location = /usr/lib/python3.8/site-packages/ansible
  ansible collection location = /home/jenkins/.ansible/collections:/usr/share/ansible/collections
  executable location = /usr/bin/ansible
  python version = 3.8.2 (default, Feb 29 2020, 17:03:31) [GCC 9.2.0]
  jinja version = 2.11.1
  libyaml = False
```


### Configuration

```console
(none)
```


### OS / Environment

Controller:
* Alpine 3.11.2
* Python 3.8

Target hosts:
* CentOS 7.9
* Python 2.7

### Steps to Reproduce

* Run an empty playbook (in debug mode) that only gathers facts against a very large number of hosts.
* Intermittently, on a small number of hosts, mount point fact gathering will fail due to `KeyError: 'LC_ALL'`

### Expected Results

Fact gathering should not fail due to multi-threaded `os.environ` mutation

### Actual Results

Mount point fact gathering fails and mount point facts are not available


### Code of Conduct

- [X] I agree to follow the Ansible Code of Conduct
return safe_eval(value, locals, include_exceptions)
    def _load_params(self):
        ''' read the input and set the params attribute.
        This method is for backwards compatibility.  The guts of the function
        were moved out in 2.1 so that custom modules could read the parameters.
        '''
        
        self.params = _load_params()
    def _log_to_syslog(self, msg):
        if HAS_SYSLOG:
            try:
                module = 'ansible-%s' % self._name
                facility = getattr(syslog, self._syslog_facility, syslog.LOG_USER)
                syslog.openlog(str(module), 0, facility)
                syslog.syslog(syslog.LOG_INFO, msg)
            except TypeError as e:
                self.fail_json(
                    msg='Failed to log to syslog (%s). To proceed anyway, '
                        'disable syslog logging by setting no_target_syslog '
                        'to True in your Ansible config.' % to_native(e),
                    exception=traceback.format_exc(),
                    msg_to_log=msg,
                )
    def debug(self, msg):