'DELETE /api/workflows/{workflow_id}/invocations/{invocation_id}
Cancel the specified workflow invocation.
:param  workflow_id:      the workflow id (required)
:type   workflow_id:      str
:param  invocation_id:      the usage id (required)
:type   invocation_id:      str
:raises: exceptions.MessageException, exceptions.ObjectNotFound'

@expose_api
def cancel_invocation(self, trans, workflow_id, invocation_id, **kwd):

    decoded_workflow_invocation_id = self.decode_id(invocation_id)
    workflow_invocation = self.workflow_manager.cancel_invocation(trans, decoded_workflow_invocation_id)
    return self.__encode_invocation(trans, workflow_invocation)
