Virtuozzo SDK interface doesn't differ filesystems from disks and sees them as disks.
Before, we always mistakenly presented disks based on files as filesystems, which is
not completely correct. Now we are going to show either disks or filesystems depending
on a hint, which uses boot device section of VZ config. Though this information
doesn't change booting order of a CT, it is used by vz libvirt interface as a hint
for libvirt representation of disks. Since now, if we have filesystems in input xml,
then we add them to VZ booting devices list and rely on this information to show
corresponding libvirt xml.
Signed-off-by: NMaxim Nestratov <mnestratov@virtuozzo.com>