importVm (shared/local storage adoption): ROOT volume always gets deviceId 1, not 0

## Description

When adopting an existing disk with `importVm importsource=shared` or `importsource=local`, the ROOT
volume ends up with `deviceid=1` instead of `0`. This happens no matter which storage backend is used —
I saw it with RBD, Linstor, and plain qcow2 on NFS, all the same way.

It doesn't stop the VM from working. It boots fine, the disk is correct, everything else is normal. But
`deviceid=1` for a ROOT volume is unexpected, and any code (or person reading `listVolumes` output) that
assumes ROOT = device 0 will get confused here.

## Where it comes from

`server/src/main/java/org/apache/cloudstack/vm/UnmanagedVMsManagerImpl.java`, in the method that handles
the shared/local KVM import:

```java
long deviceId = 1L;
if (ImportSource.SHARED == importSource) {
diskProfileStoragePoolList.add(importKVMSharedDisk(userVm, diskOffering, Volume.Type.ROOT,
template, deviceId, poolId, diskPath, diskProfile));
} else if (ImportSource.LOCAL == importSource) {
diskProfileStoragePoolList.add(importKVMLocalDisk(userVm, diskOffering, Volume.Type.ROOT,
template, deviceId, hostId, diskPath, diskProfile));
}
```

`deviceId = 1L` is passed straight into the ROOT volume's own import call.

Compare this to the other two import paths in the same file (external/VMware import and staged import).
Both of those do it the right way: ROOT is imported with `deviceId=null` (which defaults to 0), and only
the loop that comes *after*, for data disks, starts counting at `deviceId = 1L`.

In the shared/local path there is no data-disk loop at all right now (data disks aren't imported this
way yet), so it looks like the `1L` that was meant for "first disk after ROOT" ended up being used for
ROOT itself by mistake.

## History

This is not new. `git log -S "importKVMSharedDisk"` traces it back to the original "KVM Ingestion -
Import Instance" PR (#7976), so it's been there since shared/local KVM import was first added.

## Suggested fix

Pass `null` (or `0`) as the deviceId for the ROOT volume in `importKVMSharedDisk` /
`importKVMLocalDisk`, the same way the external/VMware import path already does it.

## Reproduce

```
importVm importsource=shared hypervisor=KVM storageid= diskpath= networkid= ...
```

Then check `listVolumes` for the resulting VM — ROOT shows `deviceid: 1`.

Iniziare da server/src/main/java/org/apache/cloudstack/vm/UnmanagedVMsManagerImpl.java e ispezionare il metodo di importazione KVM condiviso/locale, in particolare il deviceId passato a importKVMSharedDisk e importKVMLocalDisk. Confrontare i percorsi di importazione external/VMware e staged, quindi verificare che un volume ROOT importato riporti deviceid 0, mentre il comportamento di importazione esistente rimanga invariato.

Scritto dal modello di indicizzazione a partire dal testo della issue.