Make installation simpler -- just "vagrant up"

PR includes a couple changes which should make installation simpler and more universally correct. For example:

  - don't use a Debian mirror in China
  - get a more recent puppet in the VM by using vagrant box from puppetlabs
  - configure Vagrant to do the bootstrapping (installing modules, downloading and adding box if necessary)

Though these are steps in the right direction, it still doesn't working. Remaining issues I know about:

  - nothing actually installs phabricator. I guess it's intended for someone to put something in `/vagrant/webroot`, but I'm not exactly sure what.
  - puppet attempts to install `mysql` before doing an `apt-get update`, so many of the packages are 404. This is probably a matter of adding the right resource dependency somewhere in the manifest, but I didn't dig deeply enough to figure it out.