When running CQLSH with file input, exit with error status code if script fails

Just thought it would be nice if the cqlsh process would exit with an error status code if there are errors in the script, since it is the only thing the cqlsh process does when executing.

Preferably a predictable status code could be used for a script error to discern it from some other odd error (i.e., don't use `1` because that could be many things). Maybe `2` or something.