sync_slurm_acct issue with too many cancel jobs

[stdweird]

• the current limit when bunch of jobs are not cancelled (adn sync stops) is not configurable
• probably needs 2 limits: one on number of unique users involved and 2nd on total number of cancel commands. also the log mesage needs to be fixed (it report number of cancel commands, not number of users involved)
• if possible, we should add new users; even if this limit is reached (so it still fails, and nobody is removed/jobs cancelled; but should not block new accoutns given access)

[stdweird]

it should also only generate scancel commands for users iwth running jobs, to check eg sacct -L -s r -u vscxyz

[stdweird]

also, when users are being moved to different vo, perhaps first remove then from old VO, and then add them to new one (now, it will add you to new vo, and then try to delete it, which might fail)