time comparison filter didn't support time zone offset

[wanghao]

Cinder has supported filtering volumes by time comparison operators.
The time format is following ISO 8601. But there is small bug that didn't consider the time zone offset well in time string.
That will impact the result of filtering volumes.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.opendev.org/734415

[Sean McGinnis (sean-mcginnis)]

I don't believe this is a bug. Cinder handles everything in UTC. It was never intended to include the timezone offset in the filtering feature.

[wanghao (wanghao749)]

I found this issue when I was working on time comparison filters for snapshots. I got the updated_at time from snapshot object, it's "datetime.datetime(2020, 7, 6, 3, 47, 47, 24856, tzinfo=datetime.timezone.utc)", and when I passed this time to getting snapshots url, the query string will be '/v3/snapshots?updated_at=gt:2020-07-06 03:47:47.024856+00:00'. Of course, it UTC time. But I think since we follow the ISO 8601 time format, that's huge possibility that user pass the time string with timezone offset and now Cinder will raise an exception for it. Since we missed this feature in U cycle, (sorry my fault), we must fix it in U and V cycles both. That's why I proposed a bug fixing here.