Add simple caching for kpy bash

[akhanf]

If the cache doesn't exist (or if reset flag is used), a kpy_cache.sh script is created that initializes KSLURM_COMPUTE_NODES and PIP_WHEEL_DIR. I use another file to store the list of nodes since it was quite long to encode inline.

Kept everything else identical (just moved to the cache generation).

[pvandyken]

The reason I never cached initially was because I was concerned about graham updating their node list, and then we wouldn't be aware of nodes without internet. I wonder if a reasonable compromise is to recompute the cache once a week or so (i.e. if the cache file is older than a week old)

[akhanf]

Yes I think re-generating the cache if it is over 7 days old is good enough! I'll try that out (just looking at file modification times) once graham starts behaving again..