Allows the user to create an object without file

Now the user can create an Object without providing an actual file
in the containers view. This will submit an object with 0 bytes size.
Additionally, the 'Download' button will not be available for objects
with 0 bytes size.

Implements: blueprint metadata-only-object
Change-Id: Ib2ff2462b73d16c971ad0dfc60aaae1b0bbf0924
Document the IMAGE_LIST_FILTER_TENANTS setting

This has been around since Grizzly.

Change-Id: I1e3d3f3aaf2c0d6d7698572a1efbae9acb3e0a3e
Partial-Bug: #1221115
Give no background color to the pie charts

Currently, we hard-code a white background color for the pie charts.
This however is unneeded (as far as I can tell), and makes things look
ugly whenever the horizon css is changed to not have a white background.

Change-Id: Iac4fc1b9f77bddedc92eb627b22a8add88a0b35d
Remove leftovers of "# noqa"

This patch set removes leftovers of "# noqa" from imports
added to import_exceptions.

It also adds "django.test.utils.override_settings" to
import_exceptions, so a few more "# noqa" tags become
unnecessary.

Closes-Bug: #1273647

Change-Id: I39f856ac3ea371a2fcab272bbf358d0243164b6d
Merge "Document the IMAGE_LIST_FILTER_TENANTS setting"
Merge "Allows the user to create an object without file"
Merge "Remove leftovers of "# noqa""
Merge "Give no background color to the pie charts"