Clean up package script

* Prefer Ruby script to `gotask` script for packaging task
* Clean up Vagrant file
* Prefer `gox` to `goxc`
Add version to build artifact
Run tests as part of the packaging process
Run bootstrap script before test
Check Process.exitstatus since Process.existed? is always true
Use `IO.popen` to execute command
Build Hub in a temporary dir for cukes

We need to run the packaging script for every platform using a Vagrant box. During the packaging step, cukes are run. However, the workspace is shared between host and the Vagrant box. Instead of cleaning up the built binary for each platform, build it into a temporary dir.
Bump to Go 1.3.3 for Linux Vagrant build box
Merge pull request #634 from github/release_script

Clean up package script