Silent crash at file_handling.py

[cleevesli]

In export_ms_from_clone in file_handling.py one can successfully clone original measurement set but crash before inserting the new vis-sampled data, resulting in a model ms identical to the source data with no warning to the user. Probably occurs due to a memory error?

[ryanaloomis]

@cleevesli is testing to see if its a memory error due to insufficient memory request on cluster. Regardless, file_handling.py functions should eventually be migrated to proper try/except or assert statements to prevent future silent crashes.