improved kremlin CI

[msprotz]

• [ ] it'd be great to have a d8 binary to download as part of travis to check that the wasm target in kremlin is not broken

if @tahina-pro build a d8 binary in the docker images, can we put a tarball somewhere that I can download, with a statically-linked d8 binary for ubuntu 16.04? happy to change .ci/script.sh afterwards

• [ ] get the everest script to check & download the right z3 so that we can put verification of Server.fst under CI

[s-zanella]

Outdated. KreMLin is now under CI on Azure DevOps.