multi-factor priority plugin: fetch job priority information

[cmoussa1]

A great idea was brought up in a coffee call today about the plugin providing a feature to users who are interested in seeing how the priority for their job was calculated, especially if they might be wondering why their job priorities might be lower than expected. This information could contain the factors used in the priority calculation, along with their weight, that resulted in the integer priority. It could also perhaps leverage the query_cb () function and include the factors and their weights in addition to the information returned by the callback.

Currently, the query_cb () function returns an association's current fairshare value, and since that is the main determinant of a job's priority, a user can then technically figure out a priority for a given job by plugging it in to the plugin's multi-factor priority calculation:

priority = round ((100000 * fshare_factor) +
                  (10000 * queue_factor) +
                  (urgency - 16));

where fshare_factor is the association's current fair-share, queue_factor is the priority associated with a certain queue if passed in with the job (note: we also discussed in today's coffee call that while this factor does further refine a job's integer priority, it is not super relevant with Fluxion's current implementation of multiple queues since it schedules all jobs from one queue before moving on to the next), and urgency is the association's self-assigned urgency to decrease the priority of their job (a default value of 16).

I can definitely see the need for providing more information for how a user's priority is calculated as more and more factors are added to the job priority calculation, e.g the "age" factor described in #291.