Gets an attribute from an instance.

        :type instance_id: string
        :param instance_id: The Amazon id of the instance

        :type attribute: string
        :param attribute: The attribute you need information about
                          Valid choices are:

                          * instanceType|kernel|ramdisk|userData|
                          * disableApiTermination|
                          * instanceInitiatedShutdownBehavior|
                          * rootDeviceName|blockDeviceMapping

        :rtype: :class:`boto.ec2.image.InstanceAttribute`
        :return: An InstanceAttribute object representing the value of the
                 attribute requested

def get_instance_attribute(self, instance_id, attribute):
        """
        Gets an attribute from an instance.

        :type instance_id: string
        :param instance_id: The Amazon id of the instance

        :type attribute: string
        :param attribute: The attribute you need information about
                          Valid choices are:

                          * instanceType|kernel|ramdisk|userData|
                          * disableApiTermination|
                          * instanceInitiatedShutdownBehavior|
                          * rootDeviceName|blockDeviceMapping

        :rtype: :class:`boto.ec2.image.InstanceAttribute`
        :return: An InstanceAttribute object representing the value of the
                 attribute requested
        """
        params = {'InstanceId' : instance_id}
        if attribute:
            params['Attribute'] = attribute
        return self.get_object('DescribeInstanceAttribute', params,
                               InstanceAttribute, verb='POST')