vrouter: reload haproxy when cfg file is updated (#3726)

since 4.11.3, haproxy is always restarted when add/delete a lb rule.
When haproxy is started, the processes are
```
root@r-854-VM:~# ps aux |grep haproxy
root     22272  0.0  0.2   4036   668 ?        Ss   07:52   0:00 /usr/sbin/haproxy-systemd-wrapper -f /etc/haproxy/haproxy.cfg -p /run/haproxy.pid
haproxy  22274  0.0  2.3  38444  5856 ?        S    07:52   0:00 /usr/sbin/haproxy-master
haproxy  22275  0.0  0.3  38444   880 ?        Ss   07:52   0:00 /usr/sbin/haproxy -f /etc/haproxy/haproxy.cfg -p /run/haproxy.pid -Ds
```
When haproxy is reload, the processes are
```
root@r-854-VM:~# ps aux |grep haproxy
root     22272  0.0  0.2   4168   632 ?        Ss   07:52   0:00 /usr/sbin/haproxy-systemd-wrapper -f /etc/haproxy/haproxy.cfg -p /run/haproxy.pid
haproxy  22283  0.0  2.3  38444  5884 ?        S    07:53   0:00 /usr/sbin/haproxy-master
haproxy  22286  0.0  0.3  38444   880 ?        Ss   07:53   0:00 /usr/sbin/haproxy -f /etc/haproxy/haproxy.cfg -p /run/haproxy.pid -Ds -sf 22275
```

We need to change the pid file from /var/run/haproxy.pid to /run/haproxy.pid, so the haproxy will be reloaded instead of restarted.

Author: ustcweizhou

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

@@ -45,7 +45,7 @@ def process(self):
         if not file2.compare(file1):
             CsHelper.copy(HAPROXY_CONF_T, HAPROXY_CONF_P)
 
-            proc = CsProcess(['/var/run/haproxy.pid'])
+            proc = CsProcess(['/run/haproxy.pid'])
             if not proc.find():
                 logging.debug("CsLoadBalancer:: will restart HAproxy!")
                 CsHelper.service("haproxy", "restart")