Cache qstat output in the infosys to reduce number of requests to PBS
In the old PBS.pm code the
qstat command had been triggered per each queue several times to collect different kind of stats.
This code rework trigger
qstat only twice (jobs and queue info respectively) and store the already parsed structure for further reuse.
Fixes the issue reported on the mailing list and during NorduGrid 2019 conference (Salomon HPC ).