Allow build to continue if rebase fails
Allow build to continue if rebase fails

Test Plan:
- Canvas / docker-image passes

Change-Id: Ie1653a521121eaafedf392d165fd38f41cd785fc
Reviewed-on: https://gerrit.instructure.com/188989
Tested-by: Jenkins
Reviewed-by: Robert Lamb <bf934bf7cdbebe5899399a138c0cb75c4d783999@instructure.com>
QA-Review: Derek Bender <d24d8a7ee520e34b1cec38800225d9f36b552df7@instructure.com>
Product-Review: Derek Bender <d24d8a7ee520e34b1cec38800225d9f36b552df7@instructure.com>

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