Travis: Add a tool to print timestamp in front of log messages

[alexcrichton]

Often when debugging travis logs it's difficult to see how long everything is taking as we only time some steps, not all. Additionally there's not a lot of information to see how long it takes between steps.

It'd be awesome if we had a tool where we basically wrapped the entire build (src/ci/run.sh) in a process that simply prepended all stdout/stderr messages with a relative timestamp. AppVeyor does this by default (has a timestamp for each log line message) but unfortunately Travis doesn't.

Apparently Julia has something like this which ends up looking like https://travis-ci.org/JuliaLang/julia/jobs/211627387#L370 which is basically exactly what we'd want.

[tfheen]

You probably just want to use ts from moreutils for this. (This is what Julia does.)