We need to use the same VirtualBox Guest Additions ISO in both sp1 and
sp2, and instead of duplicating part of the installation logic, from
where to get the original files, just install the ISO on the target,
so that we can then copy it to sp2 and install it from there.
Change-Id: If1b6d0c4609be8504ff2d1bfcb0d9d7e36897539