Restructure rpc framework between neutron-server and agents

There are too many races between neutron server and agents.

For instance, create and delete Race workflow:

------neutron server side------
1. Resource create api
2. Create DB record
3. Scheduler/send RPC to agent

------agent side------
1. Get New resource notification
2. Retrieve resource info via rpc

------neutron server side------
1. Get/deal with some info of the resource
2. Get/deal with some info of the resource
*3. Delete API call comes
*4. Delete all info of the the resource
5. Get/deal with some info of the resource, oops, exception raised

------agent side------
1. Get failure notification
2. stale/trash data lives