Provide explicit image create value in Registry v2 Client test

Assign an explicit created_at datetime value to image db fixtures,
it be used to fixes race condition in Registry v2 Client test cases.

Closes-Bug: #1272136
Change-Id: Ib9f1c7072c6ac828479c6a2e5bddd0f3ad057653
Signed-off-by: Zhi Yan Liu <zhiyanl@cn.ibm.com>
Fix indentation errors found by Pep8 1.4.6+

As a preparation in order to switch to a newer
Pep8 version in the future, fix the indentation errors
that are missed by Pep8 1.4.5 due to bugs.

Change-Id: I30acf8fdc1ae7eadcbc1849409c989c2422f0f8f
Closes-Bug: #1267994
Move scrubber outside the store package

Glance's scrubber was created under the store package because it is
intended to clean up images from stores when `delayed_delete` is
enabled. However, it doesn't really belong there.

Soft delete is a Glance feature that allows images to be deleted
asynchronously as opposed of blocking clients requests during the image
deletion. Therefore, it needs to be store agnostic and live within
Glance's codebase.

Partially-Implements blueprint: create-store-package

Change-Id: I25ddbe1f0f1191f33d814dbae5788da7d511773a
Merge "Move scrubber outside the store package"
Merge "Provide explicit image create value in Registry v2 Client test"
Merge "Fix indentation errors found by Pep8 1.4.6+"