refactor: extract methods from kaltura add_media_files

 * build_partner_data handles the logic to build up the metadata JSON
    - switch to Hash#to_json in favor of string mangling
    - fan out the postfix conditionals to make the many
      conditionals in this logic more apparent
 * send_sis_data_to_kaltura? simplifies the conditional check on config
 * handle_bulk_upload_response does the optional polling for completion
   and builds media objects if the bulk upload completes
 * refresh_later DRYs up the follow on job scheduling

the too-long argument lists for these helper methods highlight the
complexity and the need for further refactoring.

so we're definitely not there yet, but this gets us another step in the
right direction.

Change-Id: I329876e64210b3a63afee3c16dd93b0f1ea96675
Reviewed-on: https://gerrit.instructure.com/39464
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Zach Pendleton <zachp@instructure.com>
Product-Review: Paul Hinze <paulh@instructure.com>
QA-Review: Paul Hinze <paulh@instructure.com>