More robust handling of NERSC outages

[weaverba137]

During NERSC outages, sometimes a night is only partially processed or not processed at all. At minimum we need a more visible warning when this does happen, and, potentially add automation to recover missing nights and exposures.

This could get complicated though, for example if the previous summary file has to always be read prior to processing the individual exposures.

There is also an issue with when any recovery would be run. If recovery is to be fully automated, do we wait for the next day, i.e. the next time the scron job runs?