We should use GetVolumeXXX api to work with volumes. This will help us to
resolve the situation with volumes without drive letter, i.e. when the
volume is mounted as a folder. Such volume is called mounted folder.
This volume is a regular mounted volume from all other points of view.
The information about non mounted volume is reported as System Reserved.
This volume is not mounted and thus it is not writable.

GuestDiskAddressList API is not used because operations are performed with
volumes but no with disks. This means that spanned disk will
be counted and handled as a single volume. It is worth mentioning
that the information about every disk in the volume can be queried
via IOCTL_VOLUME_GET_VOLUME_DISK_EXTENTS.
Signed-off-by: NOlga Krishtal <okrishtal@virtuozzo.com>
Signed-off-by: NDenis V. Lunev <den@openvz.org>
CC: Eric Blake <eblake@redhat.com>
CC: Michael Roth <mdroth@linux.vnet.ibm.com>
Signed-off-by: NMichael Roth <mdroth@linux.vnet.ibm.com>