Allow cluster to be selected by obs_*.sh scripts

[PaulHancock]

The Galaxy gpuq/workq are not technically not for our use (though practically we can still use the gpuq for a while). The two alternatives are to use the workq on either Zeus or Magnus. In order to do this we need the script templates and/or wrapper scripts to allow the cluster to be an option.

Ideas:

• default to Zeus
• default to current cluster if script is run from either magnus/zeus login node
• use -M as a cluster flag as this is inline with the slurm directive and not yet used by any of our wrapper scripts

[PaulHancock]

All changes have been implemented.