vr: fix python exception when configure VRs (#4489)

before
```
root@r-27-VM:/var/cache/cloud# /opt/cloud/bin/configure.py monitor_service.json
ERROR:root:Command 'ip link show eth0 | grep 'state DOWN'' returned non-zero exit status 1
```

with this change
```
root@r-27-VM:/var/cache/cloud# /opt/cloud/bin/configure.py monitor_service.json
root@r-27-VM:/var/cache/cloud#
```

Author: ustcweizhou

systemvm/debian/opt/cloud/bin/cs/CsHelper.py

@@ -35,7 +35,7 @@
 
 def reconfigure_interfaces(router_config, interfaces):
     for interface in interfaces:
-        cmd = "ip link show %s | grep 'state DOWN'" % interface.get_device()
+        cmd = "ip link show %s | grep ' state '" % interface.get_device()
         for device in execute(cmd):
             if " DOWN " in device:
                 cmd = "ip link set %s up" % interface.get_device()