Returns the lambda function ARN, given a name

        This requires the "lambda:GetFunction" role.

def get_lambda_function(self, function_name):
        """
        Returns the lambda function ARN, given a name

        This requires the "lambda:GetFunction" role.
        """
        response = self.lambda_client.get_function(
                FunctionName=function_name)
        return response['Configuration']['FunctionArn']