Seems like a common issue people have run into in the past. I have configured everything for VirtualBox as directed by the quick start guide, and I have tried the suggestions given in the following posts, with no luck.
You have to map vapp from the virtual box to the local machine. In order to do this, edit the hosts file (/etc/hosts) in the virtual box and add in an entry for vapp to the local loopback mapping. The line should read as follows:
127.0.0.1 vapp localhost localhost.localdomain localhost4 localhost4.localdomain4
This only take care of the UnknownHostException problem though. You may run into other other hurdles to get through such as establishing external connectivity or configuring email.