<!--- Verify first that your issue is not already reported on GitHub -->
<!--- Also test if the latest release and devel branch are affected too -->
<!--- Complete *all* sections as described, this form is processed automatically -->

##### 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


- C(cpus) CPUs accessing this NUMA node.
      - C(hostnodes) Host NUMA nodes to use.
      - C(memory) Amount of memory this NUMA node provides.
      - C(policy) NUMA allocation policy.
  onboot:
    description:
      - Specifies whether a VM will be started during system bootup.
    type: bool
    default: 'yes'
  ostype:
    description:
      - Specifies guest operating system. This is used to enable special optimization/features for specific operating systems.
      - The l26 is Linux 2.6/3.X Kernel.
    choices: ['other', 'wxp', 'w2k', 'w2k3', 'w2k8', 'wvista', 'win7', 'win8', 'win10', 'l24', 'l26', 'solaris']
    default: l26
  parallel:
    description:
      - A hash/dictionary of map host parallel devices. C(parallel='{"key":"value", "key":"value"}').
      - Keys allowed are - (parallel[n]) where 0 ≤ n ≤ 2.
      - Values allowed are - C("/dev/parport\d+|/dev/usb/lp\d+").
  pool:
    description:
      - Add the new VM to the specified pool.
  protection:
    description:
      - Enable/disable the protection flag of the VM. This will enable/disable the remove VM and remove disk operations.
    type: bool
  reboot:
    description:
      - Allow reboot. If set to C(yes), the VM exit on reboot.