Instance action's updated_at doesn't updated when action created or action event updated.

Description
===========
When we do some operation on instances, will record some
instance action(such as 'create') in 'instance_actions' table,
and some sub-event will record(such as
compute__do_build_and_run_instance) in 'instance_actions_events'
table.

The timestamp(change-since) filter will be added for filtering
the action results based on updated_at(the last time the instance
action was updated). But now the record updated time doesn't be
updated when action creating or sub-event of action updating.

So, in this patch, we need update the instance action's updated_at
when instance action events are created and instance action created
or finished.

Steps to reproduce
==================
1. Create a instances
nova boot --image 81e58b1a-4732-4255-b4f8-c844430485d2 --flavor 1 yikun

2. Look up record in instance_actions and instance_actions_events
mysql> select * from instance_actions\G
*************************** 1. row ***************************
   created_at: 2017-09-25 07:16:07
   updated_at: NULL ---> here
   deleted_at: NULL
           id: 48
       action: create
instance_uuid: fdd52ec6-100b-4a25-a5db-db7c5ad17fa8
   request_id: req-511dee3e-8951-4360-b72b-3a7ec091e7c8
      user_id: 1687f2a66222421790475760711e40e5
   project_id: 781b620d86534d549dd64902674c0f69
   start_time: 2017-09-25 07:16:05
  finish_time: NULL
      message: NULL
      deleted: 0

mysql> select * from instance_actions_events\G
*************************** 1. row ***************************
   created_at: 2017-09-25 07:16:07
   updated_at: 2017-09-25 07:16:22
   deleted_at: NULL
           id: 1
       action: create
instance_uuid: fdd52ec6-100b-4a25-a5db-db7c5ad17fa8
   request_id: req-511dee3e-8951-4360-b72b-3a7ec091e7c8
      user_id: 1687f2a66222421790475760711e40e5
   project_id: 781b620d86534d549dd64902674c0f69
   start_time: 2017-09-25 07:16:05
  finish_time: NULL
      message: NULL
      deleted: 0

Expected result
===============
Update the instance action's updated_at when instance action events
are started or finished or instance action created.

Actual result
=============
without instance aciton's updated_at