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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


balloon=dict(type='int', default=0),
            bios=dict(choices=['seabios', 'ovmf']),
            boot=dict(type='str', default='cnd'),
            bootdisk=dict(type='str'),
            clone=dict(type='str', default=None),
            cores=dict(type='int', default=1),
            cpu=dict(type='str', default='kvm64'),
            cpulimit=dict(type='int'),
            cpuunits=dict(type='int', default=1000),
            delete=dict(type='str', default=None),
            description=dict(type='str'),
            digest=dict(type='str'),
            force=dict(type='bool', default=None),
            format=dict(type='str', default='qcow2', choices=['cloop', 'cow', 'qcow', 'qcow2', 'qed', 'raw', 'vmdk']),
            freeze=dict(type='bool'),
            full=dict(type='bool', default='yes'),
            hostpci=dict(type='dict'),
            hotplug=dict(type='str'),
            hugepages=dict(choices=['any', '2', '1024']),
            ide=dict(type='dict', default=None),
            keyboard=dict(type='str'),
            kvm=dict(type='bool', default='yes'),
            localtime=dict(type='bool'),
            lock=dict(choices=['migrate', 'backup', 'snapshot', 'rollback']),
            machine=dict(type='str'),
            memory=dict(type='int', default=512),
            migrate_downtime=dict(type='int'),
            migrate_speed=dict(type='int'),
            name=dict(type='str'),
            net=dict(type='dict'),