storpool: enable direct I/O for qemu-img volume copy to secondary storage

Fix qemu-img convert failures when copying StorPool volumes to secondary
storage (NFS) during offline volume migration.

Symptom:

  Offline migration of a StorPool volume to another primary storage (e.g.
  Linstor) fails with:

    qemu-img: error while writing sector 4202495: Invalid argument

  This happens in StorPoolCopyVolumeToSecondaryCommand which creates a
  temporary StorPool snapshot, attaches it as a block device, and copies
  it via qemu-img convert to a file on NFS secondary storage.

Root cause:

  The basic QemuImg(timeout) constructor creates qemu-img convert commands
  without any I/O mode flags. On certain NFS configurations, buffered I/O
  can cause EINVAL errors at specific sector boundaries when writing large
  volumes from a raw block device source.

Fix:

  Use the 3-parameter constructor QemuImg(timeout, skipZero=false, noCache=true):

  - skipZero=false: Do NOT enable --target-is-zero. This flag is only safe
    when the target device is guaranteed pre-zeroed (e.g. thin-provisioned
    block devices like LVM_THIN or ZFS_THIN). NFS files are NOT pre-zeroed,
    so enabling this flag would cause silent data corruption by skipping
    zero-filled sectors that the target still contains stale data for.
    The Linstor storage adaptor handles this correctly by checking
    LinstorUtil.resourceSupportZeroBlocks() before enabling skipZero.

  - noCache=true: Enable direct I/O (-t none) which bypasses the kernel
    page cache. This ensures writes are flushed directly to the NFS server,
    avoiding cache-related EINVAL errors at sector boundaries and improving
    reliability for large volume copies.

Impact:

  Only affects the StorPoolCopyVolumeToSecondaryCommandWrapper code path,
  which is used during offline volume migration when StorPool is the source
  and the copy goes through secondary (NFS) storage. StorPool-to-StorPool
  copies use native StorPool cloning and are not affected.

Files:
  - MOD: plugins/storage/volume/storpool/src/main/java/com/cloud/hypervisor/
         kvm/resource/wrapper/StorPoolCopyVolumeToSecondaryCommandWrapper.java

Author: DennisKonrad

plugins/storage/volume/storpool/src/main/java/com/cloud/hypervisor/kvm/resource/wrapper/StorPoolCopyVolumeToSecondaryCommandWrapper.java

@@ -93,7 +93,7 @@ public CopyCmdAnswer execute(final StorPoolCopyVolumeToSecondaryCommand cmd, fin
                 PhysicalDiskFormat destFormat = newDisk.getFormat();
                 SP_LOG("StorpoolCopyVolumeToSecondaryCommandWrapper.execute: KVMPhysicalDisk name=%s, format=%s, path=%s, destinationPath=%s " , newDisk.getName(), newDisk.getFormat(), newDisk.getPath(), destPath);
                 QemuImgFile destFile = new QemuImgFile(destPath, destFormat);
-                QemuImg qemu = new QemuImg(cmd.getWaitInMillSeconds());
+                QemuImg qemu = new QemuImg(cmd.getWaitInMillSeconds(), false, true);
                 qemu.convert(srcFile, destFile);
 
                 final File file = new File(destPath);