Allow creation of volume-backed instance when volume quota is unlimited (no refactoring)
Overview
Fixes #940 (closed). This is a minimal fix, an alternative to !848 (merged) without any refactoring of the domain model.
Please merge either !848 (merged) or this MR, but not both.
How to Test
Log into an OpenStack project with an unlimited volume quota (unlimited number of volumes and/or unlimited total volume gibibytes). (On Jetstream2, allocation STA220003 on the Cornell region will provide this.) Ensure you can create a volume-backed instance.