Incorrect request_id field in valence response

[Lin Yang]

Current valence will contains "request_id" field in every http response as below shows. And it set to
"00000000-0000-0000-0000-000000000000" by default.

{
  "code": "Set Boot Source of Composed Node",
  "detail": "The boot source of composed node has been set to 'Hdd' with enabled state 'Once' successfully.",
  "request_id": "00000000-0000-0000-0000-000000000000"
}

However, the behavior for request_id in other openstack project is:
1. request_id should be in http header, not body
2. if request already contains this field, should add it into response header with the same id
3. if not have one, should generate new one instead of "00000000-0000-0000-0000-000000000000"