Improve preprocessing error catching

[mmccrackan]

There are some failure cases in the preprocessing functions that are not caught within those functions and therefore cause them to fail instead of returning error information, potentially with generic and less informative error message when being run from within a parallelized loop with MPI or multiprocessing. These include calls to get_meta in most of the processing or loading functions and failures within cleanup_mandb related to locked h5 files (see #1376).

These need to be wrapped in try excepts that return useful error outputs.