Add support for PartialTask list

- partial-task: Task that includes all the values except the 'Text'
columns(input, result & message).
- This patch is to have the database to return a partial-task list on users
invoking 'GET /v2/tasks'.
- Returning list of partial tasks will help in reducing the response time when the
user queries for the list of tasks.
- This patch also includes changes for making implementation and return values of
display task detail (GET /v2/tasks/{task_id}) and list tasks (GET /v2/tasks)
more explicit.

partially implements bp async-glance-workers

Change-Id: I4fbadc9a97e3147128c7c733384c7bb50918806f
Replacement mox by mock

Replace mox testing library by mock one in the file
glance/tests/unit/test_quota.py

Implements: blueprint replace-mox-with-mock

Change-Id: I4577c4debe92846ba3dd0ecf3c6bef96b4ca352c
Modify assert statement when comparing with None

Replace assertEqual(None, *) with assertIsNone in glance's
tests to have more clear messages in case of failure.

Also, replace assertTrue(* is not None) with assertIsNotNone
for the same reason.

Change-Id: If41a71bd750057c7136b03bef94c04517092134c
Closes-Bug: #1280522
Glance all: Replace basestring by six for python3 compatability

The builtin basestring abstract type was removed in python3,
use str instead, we need to using six.string_types to replace
the basestring for py3 compatibility.

Change-Id: Icf709b3499ff7f1ea935045153eb9a5ecb4618ee
Merge "Glance all: Replace basestring by six for python3 compatability"
Merge "Modify assert statement when comparing with None"
Added undescore function to some strings

Strings were not ready for translation w/o underscore function.

Change-Id: Ie6a95c4e6d6f096deddd485e3ce91bde0e9eda15
Fix logging context to include user_identity

The user_identity generated created from user, tenant, domain
user_domain and project_domain.
The new domain related values are default to None

Closes-Bug: #1283080

Change-Id: I5e43142afba3492ecf05b65ba24ee70f158f88de
Merge "Added undescore function to some strings"
Merge "Add support for PartialTask list"
Merge "Replacement mox by mock"