Abstract gerrit code checkout
Abstract gerrit code checkout

Closes: GRADE-2041

test plan:
  - spec pass
  - EDU Shared/canvas-image-wip new jenkins build passes

Change-Id: Ib28562bf5826a023091d437ccb3dca7393e4f0ce
Reviewed-on: https://gerrit.instructure.com/183249
Reviewed-by: Robert Lamb <bf934bf7cdbebe5899399a138c0cb75c4d783999@instructure.com>
Tested-by: Jenkins
QA-Review: Derek Bender <d24d8a7ee520e34b1cec38800225d9f36b552df7@instructure.com>
Product-Review: Derek Bender <d24d8a7ee520e34b1cec38800225d9f36b552df7@instructure.com>

djbender/canvas-lms,instructure/canvas-lms,sfu/canvas-lms,instructure/canvas-lms,sfu/canvas-lms,instructure/canvas-lms,instructure/canvas-lms,djbender/canvas-lms,djbender/canvas-lms,instructure/canvas-lms,sfu/canvas-lms,djbender/canvas-lms,sfu/canvas-lms,sfu/canvas-lms,instructure/canvas-lms,instructure/canvas-lms,sfu/canvas-lms,sfu/canvas-lms