[MacOS] Install script failed due to usage of sha256sum

[curzolapierre]

Following the addition of checksum (#988) check, the installation of the script is not working anymore on MacOS lacking some tools (i.e. sha256sum, wget not installed by default).

A test has been added on #1002 (issue: #1001), but it is probably not what we want to.
Either the script installs the tools or it uses other tools.

E.g. replace sha256sum by a function that use openssl:

function sha256sum() { openssl sha256 "$@" | awk '{print $2}'; }

e.g. replace wget by curl