Bump urweb-callback
Don't delete sessions immediately
Improve getNixRevision, stub for nix-expression builder
Don't use ./econat-build.sh any more. Call nix-build directly
Pass uid to the econat.nix
FFI: generate NIX representation with systemid_tonix
Fix econat/dpdk revision calculations

econat and dpdk are git submodules nowdays. Use unified mechanism to access
their hash tags.
Don't re-run failed job.
.gitignore: Add the file