### 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?

'OracleLinux': 'Oracle Linux',
        'RedHat': 'Red Hat',
        'Altlinux': 'ALT Linux',
        'ClearLinux': 'Clear Linux Software for Intel Architecture',
        'SMGL': 'Source Mage GNU/Linux',
    }
    
    OS_FAMILY_MAP = {'RedHat': ['RedHat', 'Fedora', 'CentOS', 'Scientific', 'SLC',
                                'Ascendos', 'CloudLinux', 'PSBM', 'OracleLinux', 'OVS',
                                'OEL', 'Amazon', 'Virtuozzo', 'XenServer', 'Alibaba',
                                'EulerOS', 'openEuler'],
                     'Debian': ['Debian', 'Ubuntu', 'Raspbian', 'Neon', 'KDE neon',
                                'Linux Mint', 'SteamOS', 'Devuan', 'Kali', 'Cumulus Linux',
                                'Pop!_OS', ],
                     'Suse': ['SuSE', 'SLES', 'SLED', 'openSUSE', 'openSUSE Tumbleweed',
                              'SLES_SAP', 'SUSE_LINUX', 'openSUSE Leap'],
                     'Archlinux': ['Archlinux', 'Antergos', 'Manjaro'],
                     'Mandrake': ['Mandrake', 'Mandriva'],
                     'Solaris': ['Solaris', 'Nexenta', 'OmniOS', 'OpenIndiana', 'SmartOS'],
                     'Slackware': ['Slackware'],
                     'Altlinux': ['Altlinux'],
                     'SGML': ['SGML'],
                     'Gentoo': ['Gentoo', 'Funtoo'],
                     'Alpine': ['Alpine'],
                     'AIX': ['AIX'],
                     'HP-UX': ['HPUX'],
                     'Darwin': ['MacOSX'],
                     'FreeBSD': ['FreeBSD', 'TrueOS'],
                     'ClearLinux': ['Clear Linux OS', 'Clear Linux Mix']}
    OS_FAMILY = {}