Rust build automation on the ODROID XU

[japaric]

Right now I'm bootstrapping rust using --local-rust and an old nighlty that matches the hash of the last snapshot.

To automate the build, I'll like to start from a real stage0 snapshot (just like the official buildbots). These are the requirements:

• Build a stage0 snapshot: 2015-01-27-7774359
• Wait until upstream rust starts using this snapshot (snapshot + s/range(a, b)/a..b/g + s/Show/Debug/g cleanup rust-lang/rust#21677)
• Add a script to build newer stage0 snapshots (done, but untested)
• Modify build-rust.sh to bootstrap rust from an existing snapshot (done, but untested)
• Set up a cron job