Fix checking for LVM VDO support with libblockdev 2.23 and older
Fix checking for LVM VDO support with libblockdev 2.23 and older

The check shouldn't fail when blockdev.LVMTech.VDO doesn't exist
because installed version of libblockdev is too old.

vojtechtrefny/blivet,rvykydal/blivet,rvykydal/blivet,vojtechtrefny/blivet