need to modify slurm array splitting

[afmcc]

Currently tardis prepares and launches multiple slurm array jobs so that the number
of jobs launched by each is at most 500. Unfortunately, when you get to

#SBATCH --array=9501-10000%50

on our system , it fails - i.e. I thought we needed

Upper-Lower < 10,000

but actually we need

Upper<10,000

• so will need to change the way tardis prepares and launches multiple slurm array jobs