Use just IMAGE_PREFIX, not IMAGE_PREFIX+"one"

opennebula/remotes/vmm/kvm/save.vitastor

@@ -26,7 +26,7 @@ done < <($XPATH \
     /VMM_DRIVER_ACTION_DATA/DATASTORE/TEMPLATE/POOL_NAME)
 
 VITASTOR_CONF="${XPATH_ELEMENTS[j++]}"
-IMAGE_PREFIX="${XPATH_ELEMENTS[j++]}"
+IMAGE_PREFIX="${XPATH_ELEMENTS[j++]:-one}"
 POOL_NAME="${XPATH_ELEMENTS[j++]}"
 
 CLI=vitastor-cli
@@ -37,7 +37,7 @@ if [ -n "$POOL_NAME" ]; then
     CLI="$CLI --pool ${POOL_NAME}"
 fi
 
-DST_IMAGE="${IMAGE_PREFIX}one-sys-${VM_ID}-checkpoint"
+DST_IMAGE="${IMAGE_PREFIX}-sys-${VM_ID}-checkpoint"
 
 exec_and_log "$CLI dd if=$FILE oimg=$DST_IMAGE" "Error importing checkpoint into $DST_IMAGE"
 exec_and_log "$RM -f $FILE" "Error removing checkpoint ($FILE)"