<!--- 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 -->

" only (excluding 7)." % (temp_disk_unit_number, disk_index))
                if temp_disk_unit_number == 7:
                    self.module.fail_json(msg="Invalid Disk unit number ID specified for disk at index [%s],"
                                              " please specify value other than 7 as it is reserved"
                                              "for SCSI Controller" % disk_index)
                current_disk['disk_unit_number'] = temp_disk_unit_number
            else:
                self.module.fail_json(msg="Please specify 'unit_number' under disk parameter"
                                          " at index [%s], which is required while creating disk." % disk_index)
            
            disk_type = disk.get('type', 'thick').lower()
            if disk_type not in ['thin', 'thick', 'eagerzeroedthick']:
                self.module.fail_json(msg="Invalid 'disk_type' specified for disk index [%s]. Please specify"
                                          " 'disk_type' value from ['thin', 'thick', 'eagerzeroedthick']." % disk_index)
            current_disk['disk_type'] = disk_type
            
            scsi_contrl_type = disk.get('scsi_type', 'paravirtual').lower()
            if scsi_contrl_type not in self.scsi_device_type.keys():
                self.module.fail_json(msg="Invalid 'scsi_type' specified for disk index [%s]. Please specify"
                                          " 'scsi_type' value from ['%s']" % (disk_index,
                                                                              "', '".join(self.scsi_device_type.keys())))
            current_disk['scsi_type'] = scsi_contrl_type
            disks_data.append(current_disk)
        return disks_data
    def get_recommended_datastore(self, datastore_cluster_obj):
        """
        Return Storage DRS recommended datastore from datastore cluster
        Args:
            datastore_cluster_obj: datastore cluster managed object
        Returns: Name of recommended datastore from the given datastore cluster,