fix format when adding quiz time extention

round remaining seconds calculation to ensure time format for submission
extension time over 60 minutes. also keep timer from running more than
once per refresh interval.

closes CNVS-13336

test plan:
  - create a timed quiz
  - as a student begin quiz, but do not finish / submit it
  - as instructor
    - visit quiz moderate page
    - click the clock icon / running time
    - add time using the modal window to add up to more than 60 minutes
      total time for the submission
    - click submit on the modal
    - verify that running time in the moderate table updates
      consistently

Change-Id: I2f1f6b28b130dc41795e4b30c156d40beeca56f0
Reviewed-on: https://gerrit.instructure.com/35600
Reviewed-by: Derek DeVries <ddevries@instructure.com>
Tested-by: Jenkins <jenkins@instructure.com>
QA-Review: Caleb Guanzon <cguanzon@instructure.com>
Product-Review: Jason Madsen <jmadsen@instructure.com>