As far as Virtuozzo6 and Virtuozzo7 support different disk types for virtual
machines (ploop and qcow2 respectively) and different buses (vz6: IDE, SCSI,
SATA; vz7: IDE SCSI) we add vzCapabilities structure to help undestand which
disk formats and buses are supported in the context of a current connection.
When a new connection opens, we select proper capabilities in accordance to
current Virtuozzo version.