Code cleanup needed in script.py

[sybenzvi]

The flow of control in script.py is split into several parts depending on the user environment and mode of processing. For example: code to run one exposure vs. running the exposure monitor at KPNO vs. submitting to slurm at NERSC is executed in different code blocks. Changing the order of processes thus needs to be done in several places rather than just one, which is fragile and error-prone.

Investigate if it's possible to rationalize and consolidate script.py to reduce mistakes during minor updates.