##### SUMMARY
The hostname module reports that it doesn't work on Manjaro Linux, eventhough this is simply an Arch based distribution. So I think it should work without any modification if Manjaro is 'whitelisted' as a platform that supports this module.

##### ISSUE TYPE
- Bug Report

##### COMPONENT NAME
Hostname module.

##### ANSIBLE VERSION
```ansible 2.8.3
  config file = /home/overlord/ConfigManagement/ansible/ansible.cfg
  configured module search path = ['/home/overlord/.ansible/plugins/modules', '/usr/share/ansible/plugins/modules']
  ansible python module location = /usr/lib/python3.7/site-packages/ansible
  executable location = /usr/bin/ansible
  python version = 3.7.4 (default, Jul 16 2019, 07:12:58) [GCC 9.1.0]
```

##### CONFIGURATION
<!--- Paste verbatim output from "ansible-config dump --only-changed" between quotes -->
```
ANSIBLE_NOCOWS = True
ANSIBLE_PIPELINING = True
ANSIBLE_SSH_ARGS = -C -o ControlMaster=auto -o ControlPersist=300s -o ServerAliveInterval=2
ANSIBLE_SSH_CONTROL_PATH = %(directory)s/%%h-%%r
ANSIBLE_SSH_CONTROL_PATH_DIR = /tmp/ansible-cp
COMMAND_WARNINGS = False
DEFAULT_ASK_PASS = True
DEFAULT_BECOME_ASK_PASS = True
DEFAULT_FORKS = 50
DEFAULT_GATHERING = smart
DEFAULT_HOST_LIST = ['/home/overlord/ConfigManagement/ansible/inventory']
DEFAULT_INTERNAL_POLL_INTERVAL = 0.005
DEFAULT_LOCAL_TMP = /tmp/ansible-local/ansible-local-13795g9m3yhv0
DEFAULT_MANAGED_STR = This file is managed by Ansible.%n
template: {file}
user: {uid}
host: {host}
DO NOT EDIT BY HAND!!!!
DEFAULT_POLL_INTERVAL = 15
DEFAULT_ROLES_PATH = ['/home/myuser/ConfigManagement/ansible/roles', '/home/myuser/ConfigManagement/ansible/galaxyroles', '/home/myuser/ConfigManagement/ansible/software']
DEFAULT_SSH_TRANSFER_METHOD = piped
DEFAULT_TIMEOUT = 30
DISPLAY_SKIPPED_HOSTS = False
HOST_KEY_CHECKING = False
RETRY_FILES_ENABLED = False
```

##### OS / ENVIRONMENT
Ansible host is Manjaro Linux (current version, all packages up-to-date) and the target host is localhost (in this case).


##### STEPS TO REPRODUCE
My task is:
```
- name: "Zorgen dat de hostname {{ baseline_hostname }} is"
  hostname:
    name: "{{ baseline_hostname }}"
```
This code works fine on Ubuntu based hosts on the same network, using the same role which includes this task.

##### EXPECTED RESULTS
It should work fine if a Manjaro host is seen by Ansible as an Arch Linux host.

##### ACTUAL RESULTS
```
fatal: [myhost.mydomain.local]: FAILED! => {"changed": false, "msg": "hostname module cannot be used on platform Linux (Manjaro)"}
```

module = AnsibleModule(
        argument_spec=dict(
            name=dict(type='str', required=True),
            use=dict(type='str', choices=STRATS.keys())
        ),
        supports_check_mode=True,
    )
    hostname = Hostname(module)
    name = module.params['name']
    current_hostname = hostname.get_current_hostname()
    permanent_hostname = hostname.get_permanent_hostname()
    changed = hostname.update_current_and_permanent_hostname()
    if name != current_hostname:
        name_before = current_hostname
    elif name != permanent_hostname:
        name_before = permanent_hostname
    kw = dict(changed=changed, name=name,
              ansible_facts=dict(ansible_hostname=name.split('.')[0],
                                 ansible_nodename=name,
                                 ansible_fqdn=socket.getfqdn(),
                                 ansible_domain='.'.join(socket.getfqdn().split('.')[1:])))
    if changed:
        kw['diff'] = {'after': 'hostname = ' + name + '\n',
                      'before': 'hostname = ' + name_before + '\n'}
    module.exit_json(**kw)
if __name__ == '__main__':
    main()