core: fix copying from MBS to image domain

There is no need to reconstruct the sourceDisk as ManagedBlockDisk as it
is already of this type if the source domain is a Managed Block Storage
Domain, and it will fail later on as the conversion method createManagedBlockDiskFromDiskImage
assigns the target's id to the constructed object which is incorrect, as
this is the source disk.

Signed-off-by: Benny Zlotnik <bzlotnik@redhat.com>

backend/manager/modules/bll/src/main/java/org/ovirt/engine/core/bll/storage/disk/image/CopyManagedBlockDiskCommand.java

@@ -167,7 +167,7 @@ protected void createVolumes() {
         // Attach source to host (if source is Managed Block Storage)
         // TODO: handle failures
         if (sourceDomainType == StorageDomainType.ManagedBlockStorage) {
-            String sourcePath = attachVolume(createManagedBlockDiskFromDiskImage(sourceDisk));
+            String sourcePath = attachVolume((ManagedBlockStorageDisk) sourceDisk);
             getParameters().setSourcePath(sourcePath);
         }
     }