canvas kaltura gem

fixes CNVS-10479

test plan:
  - in a course with kaltura enabled
    - go to a discussion and add media
    - upload a video (use right tab, not the webcam)
    - save the video/discussion post
    - the video should be saved properly and viewable
      (this sometimes takes a minute of two)

Change-Id: I40b9174807707dd1fb41125e04705422a8711d5d
Reviewed-on: https://gerrit.instructure.com/32024
Tested-by: Jenkins <jenkins@instructure.com>
QA-Review: Nathan Rogowski <nathan@instructure.com>
Reviewed-by: Simon Williams <simon@instructure.com>
Product-Review: Simon Williams <simon@instructure.com>