Add lock/unlock action record

Now we can show most of action on the server, it's very useful for audit, but what a pity is that we can't show lock actions. Sometimes our admin want to know who/why lock the server. It may be a good design to record lock action to action list. Here is a demo example:

nova instance-action-list 941ed017-625d-4bb9-84e5-0530ed35cefb
+--------+------------------------------------------+---------+----------------------------+
| Action | Request_ID | Message | Start_Time |
+--------+------------------------------------------+---------+----------------------------+
| create | req-41c72cc5-ddaa-4c47-a591-1ef249157518 | - | 2016-11-10T12:37:47.000000 |
| lock | req-3456a757-18d4-4cac-8c69-96a46c7f80b4 | - | 2016-11-11T05:38:25.000000 |
| unlock | req-9cc9dd48-bad3-487a-8ab6-27305cb34ab6 | - | 2016-11-11T05:38:32.000000 |
+--------+------------------------------------------+---------+----------------------------+

$ nova instance-action 941ed017-625d-4bb9-84e5-0530ed35cefb req-3456a757-18d4-4cac-8c69-96a46c7f80b4
+---------------+------------------------------------------+
| Property | Value |
+---------------+------------------------------------------+
| action | lock |
| events | [] |
| instance_uuid | 941ed017-625d-4bb9-84e5-0530ed35cefb |
| message | - |
| project_id | 66124df8b15b46dead4bff69ab35cdfb |
| request_id | req-3456a757-18d4-4cac-8c69-96a46c7f80b4 |
| start_time | 2016-11-11T05:38:25.000000 |
| user_id | 24d97e40fec0477bb75fdd8660a7b66f |
+---------------+------------------------------------------+

it shouldn't affect previous interfaces.