Failed bib records file overwritten for each file in bib transformation task

[branchedelac]

The unique name of the file, "failed_bib_records_iteration_YYYYMMDD.mrc" is assigned once for the entire task, but the file is actually opened/created anew for every data file included in the task.

The result is that the failed records from data file 1 will be overwritten by those in data file 2, and so on.

[bltravis]

I've created a branch for this fix. Will try to submit the pull request on Thursday. Need to test it with sample data.