Think through error handling for failed exposures.

r1 had a persistent error from INSTRM-1282, and the ccd wipe command was failing. Presumably based on some earlier recoverable error, sps attempted recovery by sending the clearExposure command, and the iic sequence continued with b1 generating data.

We should think though how we want to handle such failures: when they should stop everything, and when a sequence should continue. 1 of 2 cameras is different from 1 of 12.