Implement multiple postinstall scripts with a reboot at the end of postinstall.sh. This allows us to upgrade the kernel on the first pass and install the VBox tools after the reboot to ensure the DKMS get built against the new kernel.

Requires a bit of hackery to veewee itself to get it working. See https://github.com/juliandunn/veewee/commit/db5022d7723090e08926c486919016892e44b8dc for a possible solution.