Fix for Issue with creating instances on Virtual Box

Hi, 

I came across the same issue that other's seem to have with being unable to create instances, where an error similar to below was being thrown:
```
user=> (def my-machine (instance my-server "my-vmfest-vm" :debian-6.0.2.1-64bit-v0.3 :micro))
ExceptionInfo throw+: {:origin-component "", :text "", :error-code 2147942487,
:original-message "VirtualBox error:  (0x80070057)", :original-error-type :E_INVALIDARG,
:cause #<VBoxException org.virtualbox_4_1.VBoxException: VirtualBox error:  (0x80070057)>,
:type :vbox-runtime, :message "SATA device, SATA port, IDE port or IDE slot out of range, or file or UUID not found.",
:full-message "SATA device, SATA port, IDE port or IDE slot out of range, or file or UUID not found.: VirtualBox error:  (0x80070057)",
:origin-id "00000000-0000-0000-0000-000000000000"} 
```

Dug around a bit then realised that an older version is being found. Simple fix in the end :)

Cheers.