[Kimchi-devel] Support async task query classification

[Royce Lv]

Problems to solve:

     When we generate the debug reports (or upload/download a storage 
volume), only the request initiator gets task id, and is able to query 
task status. We need other users from other browser to have same view as 
the initiator, which is not possible now.

Solution:
     1. We add async event information, events will also be classified 
so that users can subscribe events interest them

     2. We enable reverse mapping (task to resource which generate them) 
query for users. So that user can find tasks related to a collection:
     GET /tasks?init_collection=debugreports
     after take a look at current implementation, we can also query 
taget_uri
     GET /tasks?target_uri=r(^/debugreports/*) (need to be encoded)

Since we currently out of support of async events, we may want to add 
task query for this purpose.

Welcome comments!