Slurm change

What does this MR do?

MR includes changes to slurm.go where we use sacct for polling jobs to get their status and also refactors slurm.go. Also adds additional tests in slurm_test.go

Why was this MR needed?

MR needed because the previous approach of using squeue is not the right approach and could lead to the slurm controller being overloaded.

Are there points in the code the reviewer needs to double check?

Already double checked in golang-hpc repo.