delete deleted image 500 bug

Fixes bug 1138666

When you delete an image that you just deleted, you get a 500 Internal Server Error.
In this case, the problem isn't an internal server error but the "unauthorized" response
from the image service is not expected.

This can be recreated with devstack:
 1) delete an image
 2) delete the same image

Here's an example:

$ nova image-list
+--------------------------------------+---------------------------------+--------+--------+
| ID                                   | Name                            | Status | Server |
+--------------------------------------+---------------------------------+--------+--------+
| caa6c969-0f32-466b-8e8e-a7e0ac835470 | cirros-0.3.1-x86_64-uec         | ACTIVE |        |
| 8af603da-b69f-49c6-8e52-25632eccb31c | cirros-0.3.1-x86_64-uec-kernel  | ACTIVE |        |
| fe67d4e1-baca-4968-8638-2314373b620b | cirros-0.3.1-x86_64-uec-ramdisk | ACTIVE |        |
+--------------------------------------+---------------------------------+--------+--------+

$ nova image-delete caa6c969-0f32-466b-8e8e-a7e0ac835470

$ nova image-delete caa6c969-0f32-466b-8e8e-a7e0ac835470
ERROR: The server has either erred or is incapable of performing the requested operation. (HTTP 500) (Request-ID: req-1254f8a5-8dda-444a-a077-2072ab3baa6a)

If you delete a deleted image, the server should respond with '403 Forbidden'
because the image still exists and no user is allowed to delete a deleted image.

The fix is to catch the exception from the image service and
convert it to a wsgi exception for '403 Forbidden'.

Change-Id: I2f14687d5468b67389f5dd6ab338ceb54e8a29bb
Add ability to control max utilization of a cell

Add a 'reserve_percent' config flag to cells to control the
maximum free capacity that a child cell will be advertised to its
parent(s).

This gives the ability to leave some reserve capacity
in child cells for operational maintenance.

Change-Id: I1dae1eae4f61ca8079c6f24e60176c31fd8a759d
Merge "delete deleted image 500 bug"
Merge "Add ability to control max utilization of a cell"