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##### SUMMARY
An hour ago I upgraded my Proxmox to the new stable version 6. Since then my playbooks fail with this error:
`fatal: [proxmox]: FAILED! => {"changed": false, "msg": "authorization on proxmox cluster failed with exception: could not convert string to float: '6.0-4'"}`

It seems like the proxmox changed the API.

##### ISSUE TYPE
- Bug Report

##### COMPONENT NAME
proxmox (https://github.com/mrdrogdrog/ansible/blob/6430205d396b7c1733de22a898c51823f67d5bf4/lib/ansible/modules/cloud/misc/proxmox.py#L484)

##### ANSIBLE VERSION
<!--- Paste verbatim output from "ansible --version" between quotes -->
```
ansible 2.8.2
  config file = /etc/ansible/ansible.cfg
  configured module search path = ['/home/tilman/.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 = 3.7.3 (default, Jun 24 2019, 04:54:02) [GCC 9.1.0]
```


##### OS / ENVIRONMENT
Proxmox 6 


##### STEPS TO REPRODUCE
- Use the latest ansible version
- Use the latest stable version of proxmox (6)
- Use the proxmox module to do anything. E.g. create a container
- Get the error


##### EXPECTED RESULTS
Normal runthrough

##### ACTUAL RESULTS
Crash with an error


validate_certs=dict(type='bool', default='no'),
            vcpus=dict(type='int', default=None),
            vga=dict(default='std', choices=['std', 'cirrus', 'vmware', 'qxl', 'serial0', 'serial1', 'serial2', 'serial3', 'qxl2', 'qxl3', 'qxl4']),
            virtio=dict(type='dict', default=None),
            vmid=dict(type='int', default=None),
            watchdog=dict(),
        ),
        mutually_exclusive=[('delete', 'revert'), ('delete', 'update'), ('revert', 'update'), ('clone', 'update'), ('clone', 'delete'), ('clone', 'revert')],
        required_one_of=[('name', 'vmid',)],
        required_if=[('state', 'present', ['node'])]
    )
    if not HAS_PROXMOXER:
        module.fail_json(msg='proxmoxer required for this module')
    api_user = module.params['api_user']
    api_host = module.params['api_host']
    api_password = module.params['api_password']
    clone = module.params['clone']
    cpu = module.params['cpu']
    cores = module.params['cores']
    delete = module.params['delete']
    memory = module.params['memory']
    name = module.params['name']
    newid = module.params['newid']
    node = module.params['node']
    revert = module.params['revert']
    sockets = module.params['sockets']
    state = module.params['state']
    timeout = module.params['timeout']
    update = bool(module.params['update'])
    vmid = module.params['vmid']