volume.go
func (c *Client) ListVolumes(dcid string) (*Volumes, error) {
	url := volumeColPath(dcid) + `?depth=` + c.client.depth
	ret := &Volumes{}
	err := c.client.Get(url, ret, http.StatusOK)
	return ret, err
}
func (c *Client) ListVolumes(dcid string) (*Volumes, error) {
	url := volumeColPath(dcid) + `?depth=` + c.client.depth
	ret := &Volumes{}
	err := c.client.Get(url, ret, http.StatusOK)
	return ret, err
}
// ListVolumes returns a Collection struct for volumes in the Datacenter