Invalid validation for unlimited values when updating user quota

[Gastón Severina]

There is a possible scenario that is not correctly handled when validating quota limit. If the remaining quota is unlimited (-1) and new quota value is unlimited (-1) then both values are summed resulting in a -2 value that then causes the following error: "Quota limit must be greater than 0".

[Christopher Yeoh (cyeoh-0)]

It looks like we have a general problem with estimating what the maximum quota can be if it is currently unlimited. Needs further investigation for more than just this specific case (I think we'll often have off by one errors).

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/80615
Committed: https://git.openstack.org/cgit/openstack/nova/commit/?id=362e998e89a1f1d9dce3379c4610b205ebeec7c0
Submitter: Jenkins
Branch: master

commit 362e998e89a1f1d9dce3379c4610b205ebeec7c0
Author: gseverina <email address hidden>
Date: Fri Mar 14 13:06:45 2014 -0300

    Handling unlimited values when updating quota

    Changes:
    - Adding a general approach to handle unlimited values when performing
    calculations with quota values.
    - New test that fails without the fix.
    - Updated test cases to support the fix.

    Change-Id: I762a8e67261c0e0286307832cd13ad12e6d96504
    Closes-Bug: #1292494