'GET /api/workflows/{workflow_id}/invocations/{invocation_id}
Get detailed description of workflow invocation
:param  workflow_id:        the workflow id (required)
:type   workflow_id:        str
:param  invocation_id:      the invocation id (required)
:type   invocation_id:      str
:raises: exceptions.MessageException, exceptions.ObjectNotFound'

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

    decoded_workflow_invocation_id = self.decode_id(invocation_id)
    workflow_invocation = self.workflow_manager.get_invocation(trans, decoded_workflow_invocation_id)
    if workflow_invocation:
        return self.__encode_invocation(trans, workflow_invocation, step_details=kwd.get('step_details', False))
    return None
