qemuMonitorTextAddDrive: Fail on unrecognized disk format

Since qemu commit 3ef6c40ad0b it can fail if trying to hotplug a
disk that is not qcow2 despite us saying it is. We need to error
out in that case.
Signed-off-by: NMichal Privoznik <mprivozn@redhat.com>
Reviewed-by: NJohn Ferlan <jferlan@redhat.com>

src/qemu/qemu_monitor_text.c

@@ -1963,6 +1963,12 @@ int qemuMonitorTextAddDrive(qemuMonitorPtr mon,
         goto cleanup;
     }
 
+    if (strstr(reply, "Image is not in")) {
+        virReportError(VIR_ERR_OPERATION_FAILED, "%s",
+                       _("Incorrect disk format"));
+        goto cleanup;
+    }
+
     ret = 0;
 
  cleanup: