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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 = module.params['validate_certs']
    # If password not set get it from PROXMOX_PASSWORD env
    if not api_password:
        try:
            api_password = os.environ['PROXMOX_PASSWORD']
        except KeyError as e:
            module.fail_json(msg='You should set api_password param or use PROXMOX_PASSWORD environment variable')
    try:
        proxmox = ProxmoxAPI(api_host, user=api_user, password=api_password, verify_ssl=validate_certs)
        global VZ_TYPE
        global PVE_MAJOR_VERSION
        PVE_MAJOR_VERSION = 3 if float(proxmox.version.get()['version']) < 4.0 else 4
    except Exception as e:
        module.fail_json(msg='authorization on proxmox cluster failed with exception: %s' % e)
    # If vmid not set get the Next VM id from ProxmoxAPI
    # If vm name is set get the VM id from ProxmoxAPI
    if not vmid:
        if state == 'present' and (not update and not clone) and (not delete and not revert):
            try:
                vmid = get_nextvmid(module, proxmox)
            except Exception as e:
                module.fail_json(msg="Can't get the next vmid for VM {0} automatically. Ensure your cluster state is good".format(name))
        else:
            try:
                if not clone:
                    vmid = get_vmid(proxmox, name)[0]
                else:
                    vmid = get_vmid(proxmox, clone)[0]
            except Exception as e:
                if not clone: