try to login guest via all nics after driver installed

after nic driver installed default route maybe change, so
try to login guest via all nic to avoid login timeout issue.
Signed-off-by: NXu Tian <xutian@redhat.com>

qemu/tests/win_virtio_update.py

@@ -24,6 +24,19 @@ def run(test, params, env):
     :param params: Dictionary with the test parameters
     :param env: Dictionary with test environment.
     """
+
+    def reboot(vm, session=None):
+        nic_idx = len(vm.virtnet) - 1
+        while nic_idx >= 0:
+            try:
+                return vm.reboot(session, nic_index=nic_idx)
+            except Exception:
+                nic_idx -= 1
+                if nic_idx < 0:
+                    raise
+                logging.warn("Unable to login guest, "
+                             "try to login via nic %d" % nic_idx)
+
     def check_cdrom(timeout):
         cdrom_chk_cmd = "echo list volume > cmd && echo exit >>"
         cdrom_chk_cmd += " cmd && diskpart /s cmd"
@@ -195,7 +208,7 @@ def run(test, params, env):
             cmd = re.sub("WIN_UTILS", vol_utils, install_cmds[driver])
             cmd = re.sub("WIN_VIRTIO", vol_virtio, cmd)
             session.cmd(cmd, timeout=driver_install_timeout)
-            session = vm.reboot(session)
+            session = reboot(vm, session)
 
     if params.get("check_info") == "yes":
         fail_log = "Details check failed in guest."