Exhaustivity check in rust backend

The MR main purpose is to move exhaustivity checks in a module shared by all backends and to use the check in rust backend.

it also comes with two almost unrelated changes : reordering of blacklisted instruction (which helps readability) and a target to git reset tezos-on-tezos workdir which is simpler than redownloading the full repo. Beware that this could in some circumstances reset polyrun repo !