CLC-3368 Distinguish output of incremental and batch Canvas refresh jobs

https://jira.ets.berkeley.edu/jira/browse/CLC-3368

I noticed that the incremental and the batch-term refreshes are both creating "tmp/canvas" CSV files with the same name. This isn't so much a functional issue as a diagnostic/debugging issue. It's very helpful to have a backlog of refresh script CSVs to reference when trying to figure out just how/when a student was added or dropped.