qemu.test.cfg: Add usb-hub related test

Signed-off-by: NQingtang Zhou <qzhou@redhat.com>

qemu/tests/cfg/usb.cfg

@@ -6,6 +6,7 @@
     restart_vm = yes
     kill_vm_on_error = yes
     usbs += " usbtest"
+    usb_bus = "usbtest.0"
 
     # usb controllers
     variants:
@@ -25,7 +26,16 @@
             usb_max_port_usbtest = 4
             drive_format_stg = "usb3"
 
-    # usb devices (boot+reboot tests)
+    # usb toplogy
+    variants:
+        - usb_default:
+        - with_usb_hub:
+            no usb_nodev
+            usb_devices += " hub1"
+            usb_type_hub1 = usb-hub
+            usb_port_hub1 = "2"
+            usb_port_testdev = "2.1"
+    # usb devices
     variants:
         - @usb_nodev:
             # Not used in RHEL testing.