qemu: driver: Add debug message when we conjure block job data object

Report in logs when we don't find existing block job data and create it
just to handle the job.
Signed-off-by: NPeter Krempa <pkrempa@redhat.com>
Reviewed-by: NJán Tomko <jtomko@redhat.com>

src/qemu/qemu_driver.c

@@ -4702,6 +4702,7 @@ processBlockJobEvent(virQEMUDriverPtr driver,
     }
 
     if (!(job = qemuBlockJobDiskGetJob(disk))) {
+        VIR_DEBUG("creating new block job object for '%s'", diskAlias);
         if (!(job = qemuBlockJobDiskNew(vm, disk, type, diskAlias)))
             goto endjob;
         job->state = QEMU_BLOCKJOB_STATE_RUNNING;