### SUMMARY 

[Flatcar Container Linux](https://www.flatcar-linux.org) is not properly discovered by Ansible, especially while setting hostname.

##### ISSUE TYPE
- Bug Report

##### COMPONENT NAME
hostname

##### ANSIBLE VERSION
```paste below
ansible --version
ansible 2.9.7
  config file = /etc/ansible/ansible.cfg
  configured module search path = ['.../.ansible/plugins/modules', '/usr/share/ansible/plugins/modules']
  ansible python module location = /usr/lib/python3.8/site-packages/ansible
  executable location = /usr/bin/ansible
  python version = 3.8.2 (default, Feb 28 2020, 00:00:00) [GCC 10.0.1 20200216 (Red Hat 10.0.1-0.8)]
```

##### OS / ENVIRONMENT
Guest OS: Flatcar Container Linux Alpha 2492.0.0
Host: Fedora 32

##### STEPS TO REPRODUCE
1. Clone [image builder](https://github.com/kubernetes-sigs/image-builder).
2. Adjust files for Flatcar.
3. Run `packer build`, which creates Flatcar image, provisions a host.

##### EXPECTED RESULTS
No error

##### ACTUAL RESULTS

Failure like:
```
flatcar-alpha: TASK [sysprep : Set hostname] **************************************************
    flatcar-alpha: fatal: [default]: FAILED! => {"changed": false, "msg": "hostname module cannot be  used on platform Linux (Flatcar)"}^
```

For info, in Flatcar you can see for example:
```
$ cat /etc/os-release 
NAME="Flatcar Container Linux by Kinvolk"
ID=flatcar
ID_LIKE=coreos
VERSION=2492.0.0
VERSION_ID=2492.0.0
BUILD_ID=2020-04-28-2210
PRETTY_NAME="Flatcar Container Linux by Kinvolk 2492.0.0 (Rhyolite)"
ANSI_COLOR="38;5;75"
HOME_URL="https://flatcar-linux.org/"
BUG_REPORT_URL="https://issues.flatcar-linux.org"
FLATCAR_BOARD="amd64-usr"

$ cat /etc/lsb-release 
DISTRIB_ID="Flatcar Container Linux by Kinvolk"
DISTRIB_RELEASE=2492.0.0
DISTRIB_CODENAME="Rhyolite"
DISTRIB_DESCRIPTION="Flatcar Container Linux by Kinvolk 2492.0.0 (Rhyolite)"
```

As far as I understand, so far Ansible only supported [CoreOS Container Linux](https://github.com/ansible/ansible/blob/cedfe34619128783d2a799695bd4c53d6adc9dd1/lib/ansible/module_utils/facts/system/distribution.py#L387), which will be soon EOL. Recently there was an attempt to support [Fedora CoreOS or RedHat CoreOS](https://github.com/ansible/ansible/pull/53563), which was not merged. I am not sure if there is any recent progress about that.

So would it be reasonable to simply add new code for Flatcar, just like CoreOS Container Linux?

for ddict in self.OSDIST_LIST:
            name = ddict['name']
            path = ddict['path']
            allow_empty = ddict.get('allowempty', False)
            has_dist_file, dist_file_content = self._get_dist_file_content(path, allow_empty=allow_empty)
            
            
            if has_dist_file and allow_empty:
                dist_file_facts['distribution'] = name
                dist_file_facts['distribution_file_path'] = path
                dist_file_facts['distribution_file_variety'] = name
                break
            if not has_dist_file:
                
                continue
            parsed_dist_file, parsed_dist_file_facts = self._parse_dist_file(name, dist_file_content, path, dist_file_facts)
            
            if parsed_dist_file:
                dist_file_facts['distribution'] = name
                dist_file_facts['distribution_file_path'] = path
                
                
                
                dist_file_facts['distribution_file_variety'] = name
                dist_file_facts['distribution_file_parsed'] = parsed_dist_file
                dist_file_facts.update(parsed_dist_file_facts)
                break
        return dist_file_facts
    
    def parse_distribution_file_Slackware(self, name, data, path, collected_facts):