This allows you to construct an arbitrary RPC call to retreive common stuff. For example:
        Configuration:  get: "<get-configuration/>"
        Interface information:  get: "<get-interface-information/>"
        A particular interfacece information:
              get: "<get-interface-information/>"
              child: "<interface-name>ge-0/0/0</interface-name>"

def _rpc(self, get, child=None, **kwargs):
        """
        This allows you to construct an arbitrary RPC call to retreive common stuff. For example:
        Configuration:  get: "<get-configuration/>"
        Interface information:  get: "<get-interface-information/>"
        A particular interfacece information:
              get: "<get-interface-information/>"
              child: "<interface-name>ge-0/0/0</interface-name>"
        """
        rpc = etree.fromstring(get)

        if child:
            rpc.append(etree.fromstring(child))

        response = self.device.execute(rpc)
        return etree.tostring(response)