Build: Append the date to local build names

All local runs have been so far appearing under a build called "local run",
supposedly running for 121 days now and failing. Separating runs helps with
the organization and allows to see the result of a particular run at a glance.

We could also optionally append the user name if present. Thoughts?
My preference would be to keep the ISO string as-is, possibly with `.replace( /\.\d*/, "" )`, but I approve of the overall value in timestamping jobs. User name is probably overkill, though.