Add hhvm::dev; provision on osmium

* Installs build-deps, per <https://github.com/facebook/
  hhvm/wiki/Building-and-installing-HHVM-on-Ubuntu-14.04>
* Clones operations/software/hhvm-dev (our fork, which has Tim's upstream
  patches).

Change-Id: I8cb188d069c0483eaab8bb125c23b95980dbbaf9