This leaves all the md5sum parts in place for now, but switches
to using sha256sum. Tries both shasum -a 256 and sha256sum.

Change-Id: I393d0dde56521f6e9e76f3d5a8d15c6c830fd683
Reviewed-on: https://gerrit.libreoffice.org/34633Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Norbert Thiebaud <nthiebaud@gmail.com>