vmm/virtualbox: Centralize version-compatibility code in compat class
vmm/virtualbox: Centralize version-compatibility code in compat class

- Add class containing version-compatibility wrappers for the VirtualBox
Main API, and move all version-specific tests there

- Merge detach_disk() and parse_version() into their callers

cmusatyalab/openisr,cmusatyalab/openisr,cmusatyalab/openisr,cmusatyalab/openisr,cmusatyalab/openisr