created key structure for history-like objects
added history entity for host and vm

Signed-off-by: Laszlo Hornyak <laszlo.hornyak@gmail.com>
added disk entity

Signed-off-by: Laszlo Hornyak <laszlo.hornyak@gmail.com>
- added expectations list to Disk
- added list of disks to vm

Signed-off-by: Laszlo Hornyak <laszlo.hornyak@gmail.com>