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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


module = AnsibleModule(
        argument_spec=dict(
            api_host=dict(required=True),
            api_user=dict(required=True),
            api_password=dict(no_log=True),
            vmid=dict(required=False),
            validate_certs=dict(type='bool', default='no'),
            node=dict(),
            pool=dict(),
            password=dict(no_log=True),
            hostname=dict(),
            ostemplate=dict(),
            disk=dict(type='str', default='3'),
            cores=dict(type='int', default=1),
            cpus=dict(type='int', default=1),
            memory=dict(type='int', default=512),
            swap=dict(type='int', default=0),
            netif=dict(type='dict'),
            mounts=dict(type='dict'),
            ip_address=dict(),
            onboot=dict(type='bool', default='no'),
            storage=dict(default='local'),