[FEATURE] Enable custom code in on_compute_node_configured.sh

[cartalla]

Is your feature request related to a problem? Please describe.

The compute node AMI is missing some things like packages and file system mounts and we want to be able to update the compute node without having to create a new AMI and update the cluster so we can quickly test the fixes that we need.
In order to do that it would be helpful to have a script that gets called, if it exists, as part of the on_compute_node_configured.sh script.

Describe the solution you'd like

I would like to be able to choose between running the custom actions at the beginning or end of the script so suggest calling the following two files, if they exist:

• /opt/slurm/config/bin/on_compute_node_configured_custom_prolog.sh
• /opt/slurm/config/bin/on_compute_node_configured_custom_prolog.sh