Update to Omnibus 4

:construction: 

Update push server project to Omnibus 4.  
- [ ] Clean build in CI.

Ready for review @opscode/release-engineers @manderson26 

I've been setting the user, group and password as the initial converge can become otherwise cranky on certain platforms. We also no longer need `install_dir` set. Something like this should work:

```yaml
build_user:          vagrant
build_user_group:    vagrant
build_user_password: vagrant
install_dir:         /opt/opscode-push-jobs-server
```