Add vCenter on the switch

        Args:
            id(str) : Name of an established vCenter
            url (bool) : vCenter URL
            username (str): Username of the vCenter
            password (str): Password of the vCenter
            callback (function): A function executed upon completion of the
                 method.

        Returns:
           Return value of `callback`.

        Raises:
            None

def add_vcenter(self, **kwargs):
        """
        Add vCenter on the switch

        Args:
            id(str) : Name of an established vCenter
            url (bool) : vCenter URL
            username (str): Username of the vCenter
            password (str): Password of the vCenter
            callback (function): A function executed upon completion of the
                 method.

        Returns:
           Return value of `callback`.

        Raises:
            None
        """
        config = ET.Element("config")
        vcenter = ET.SubElement(config, "vcenter",
                                xmlns="urn:brocade.com:mgmt:brocade-vswitch")
        id = ET.SubElement(vcenter, "id")
        id.text = kwargs.pop('id')
        credentials = ET.SubElement(vcenter, "credentials")
        url = ET.SubElement(credentials, "url")
        url.text = kwargs.pop('url')
        username = ET.SubElement(credentials, "username")
        username.text = kwargs.pop('username')
        password = ET.SubElement(credentials, "password")
        password.text = kwargs.pop('password')

        try:
            self._callback(config)
            return True

        except Exception as error:
            logging.error(error)
            return False