### 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
set ``close_fds`` to False.
        :kw before_communicate_callback: This function will be called
            after ``Popen`` object will be created
            but before communicating to the process.
            (``Popen`` object will be passed to callback as a first argument)
        :kw ignore_invalid_cwd: This flag indicates whether an invalid ``cwd``
            (non-existent or not a directory) should be ignored or should raise
            an exception.
        :returns: A 3-tuple of return code (integer), stdout (native string),
            and stderr (native string).  On python2, stdout and stderr are both
            byte strings.  On python3, stdout and stderr are text strings converted
            according to the encoding and errors parameters.  If you want byte
            strings on python3, use encoding=None to turn decoding to text off.
        '''
        
        self._clean = None
        if not isinstance(args, (list, binary_type, text_type)):
            msg = "Argument 'args' to run_command must be list or string"
            self.fail_json(rc=257, cmd=args, msg=msg)
        shell = False
        if use_unsafe_shell:
            
            if isinstance(args, list):
                args = b" ".join([to_bytes(shlex_quote(x), errors='surrogate_or_strict') for x in args])
            else:
                args = to_bytes(args, errors='surrogate_or_strict')
            
            if executable:
                executable = to_bytes(executable, errors='surrogate_or_strict')
                args = [executable, b'-c', args]