<!--- Verify first that your feature was not already discussed on GitHub -->
<!--- Complete *all* sections as described, this form is processed automatically -->

##### SUMMARY
<!--- Describe the new feature/improvement briefly below -->
vmware_guest_disk should propose `disk_mode` parameter (like vmware_guest module).
The playbook bellow does not raise an error but disk is always added in `persistent` mode, even I set `independent_persistent` for `disk_mode` var.
If it's a bug please could you fix it? If it's not consider it as a feature request :)

##### ISSUE TYPE
- Feature Idea (or maybe a bug)

##### COMPONENT NAME
<!--- Write the short name of the module, plugin, task or feature below, use your best guess if unsure -->
vmware_guest_disk 

##### ADDITIONAL INFORMATION
<!--- Describe how the feature would be used, why it is needed and what it would solve -->

<!--- Paste example playbooks or commands between quotes below -->
```yaml
---
- name: get vm {{ target | upper }} facts
  vmware_guest_facts:
    hostname: "{{ vcenter_hostname }}"
    username: "{{ vcenter_username }}"
    password: "{{ vcenter_password }}"
    datacenter: "{{ datacenter }}"
    validate_certs: no
    name: "{{ target | upper }}"
  register: vm_facts
  delegate_to: localhost

- name: add disk to vm {{ target | upper }}
  vmware_guest_disk:
    hostname: "{{ vcenter_hostname }}"
    username: "{{ vcenter_username }}"
    password: "{{ vcenter_password }}"
    datacenter: "{{ datacenter }}"
    validate_certs: no
    name: "{{ target | upper }}"
    disk:
      - size_gb: "{{ size_gb }}"
        type: "{{ type }}"
        disk_mode: "{{ disk_mode }}"
        scsi_controller: "{{ scsi_controller }}" 
        unit_number: "{{ unit_number }}"
        datastore: "{{ vm_facts.instance.hw_datastores | first }}"
  delegate_to: localhost
```

<!--- HINT: You can also paste gist.github.com links for larger files -->

disk_spec.device.capacityInKB))
                    if disk['size'] != disk_spec.device.capacityInKB:
                        disk_spec.operation = vim.vm.device.VirtualDeviceSpec.Operation.edit
                        disk_spec.device.capacityInKB = disk['size']
                        self.config_spec.deviceChange.append(disk_spec)
                        disk_change = True
                        results['disk_changes'][disk['disk_index']] = "Disk size increased."
                    else:
                        results['disk_changes'][disk['disk_index']] = "Disk already exists."
                elif disk['state'] == 'absent':
                    
                    disk_spec = vim.vm.device.VirtualDeviceSpec()
                    disk_spec.operation = vim.vm.device.VirtualDeviceSpec.Operation.remove
                    disk_spec.fileOperation = vim.vm.device.VirtualDeviceSpec.FileOperation.destroy
                    disk_spec.device = current_scsi_info[scsi_controller]['disks'][disk['disk_unit_number']]
                    self.config_spec.deviceChange.append(disk_spec)
                    disk_change = True
                    results['disk_changes'][disk['disk_index']] = "Disk deleted."
            if disk_change:
                
                
                self.reconfigure_vm(self.config_spec, 'disks')
                self.config_spec = vim.vm.ConfigSpec()
                self.config_spec.deviceChange = []
            disk_change_list.append(disk_change)
        if any(disk_change_list):
            results['changed'] = True
        results['disk_data'] = self.gather_disk_facts(vm_obj=self.vm)
        self.module.exit_json(**results)
    def sanitize_disk_inputs(self):