Returns distributed virtual porgroups (dvportgroups).
    The parent object can be either a datacenter or a dvs.

    parent_ref
        The parent object reference. Can be either a datacenter or a dvs.

    portgroup_names
        The names of the dvss to return. Default is None.

    get_all_portgroups
        Return all portgroups in the parent. Default is False.

def get_dvportgroups(parent_ref, portgroup_names=None,
                     get_all_portgroups=False):
    '''
    Returns distributed virtual porgroups (dvportgroups).
    The parent object can be either a datacenter or a dvs.

    parent_ref
        The parent object reference. Can be either a datacenter or a dvs.

    portgroup_names
        The names of the dvss to return. Default is None.

    get_all_portgroups
        Return all portgroups in the parent. Default is False.
    '''
    if not (isinstance(parent_ref,
                       (vim.Datacenter, vim.DistributedVirtualSwitch))):
        raise salt.exceptions.ArgumentValueError(
            'Parent has to be either a datacenter, '
            'or a distributed virtual switch')
    parent_name = get_managed_object_name(parent_ref)
    log.trace('Retrieving portgroup in %s \'%s\', portgroups_names=\'%s\', '
              'get_all_portgroups=%s',
              type(parent_ref).__name__,
              parent_name,
              ','.join(portgroup_names) if portgroup_names else None,
              get_all_portgroups)
    properties = ['name']
    if isinstance(parent_ref, vim.Datacenter):
        traversal_spec = vmodl.query.PropertyCollector.TraversalSpec(
            path='networkFolder',
            skip=True,
            type=vim.Datacenter,
            selectSet=[vmodl.query.PropertyCollector.TraversalSpec(
                path='childEntity',
                skip=False,
                type=vim.Folder)])
    else:  # parent is distributed virtual switch
        traversal_spec = vmodl.query.PropertyCollector.TraversalSpec(
            path='portgroup',
            skip=False,
            type=vim.DistributedVirtualSwitch)

    service_instance = get_service_instance_from_managed_object(parent_ref)
    items = [i['object'] for i in
             get_mors_with_properties(service_instance,
                                      vim.DistributedVirtualPortgroup,
                                      container_ref=parent_ref,
                                      property_list=properties,
                                      traversal_spec=traversal_spec)
             if get_all_portgroups or
             (portgroup_names and i['name'] in portgroup_names)]
    return items