GitLab

After discussions, the current find_queue_equivalence_classes for this
system really only complicates the codebase for very little actual gain.
After this, the system will have only one equivalence class at all times
consisting of all active queues assigned to nodes and all active
reservations.

This simplification allows us to ensure that find_job_location only gets
called twice, once for reservations, which ignore drain times, and then
immediately after for the normal "production" queue jobs, which do set
drain times.  In both cases we can just clear drain times across the
machine.

In addition to testing (and more tests coming for the case that caused
this examination to begin with), we know that this works, as any system
with a queue or set of overlapping queues across all resources on the
machine forms a single equivalence class under the old code.