deprioritize kaltura conversions with suspiciously high bitrates

we've seen some broken conversions that are 20x+ larger than
the original video.  add a quick heuristic to deprioritize any
conversion > 5x the size of the original.  (seems like if
the conversions are substantially larger than the original,
then we're doing it wrong.)

fixes CNVS-11227

Change-Id: I0b318c609ddd59f4507d38a4b69383f3ff77279c
Reviewed-on: https://gerrit.instructure.com/31442
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Bracken Mosbacker <bracken@instructure.com>
Product-Review: Bracken Mosbacker <bracken@instructure.com>
QA-Review: Nathan Rogowski <nathan@instructure.com>