VR: fix rsyslog compresses log files but not release disk space in VR (#4869)

We had critical issue with VR recently. The VRs of shared network or vpc stops working after some days.
After investigation, I found that the disk space is full

```
root@r-10-VM:~# df
Filesystem     1K-blocks    Used Available Use% Mounted on
/dev/vda5        2086316 2069932         0 100% /
```

logrotate/ryslog has compresses the log files, but space is not released. see `lsof |grep deleted`

```
root@r-10-VM:~# lsof |grep deleted
rsyslogd    960                      root   12w      REG              254,5 493060096        137 /var/log/daemon.log.1 (deleted)
rsyslogd    960                      root   13w      REG              254,5  17715200        110 /var/log/messages.1 (deleted)
rsyslogd    960                      root   16w      REG              254,5 545968128        342 /var/log/auth.log.1 (deleted)
rsyslogd    960                      root   18w      REG              254,5  38313984        341 /var/log/cron.log.1 (deleted)
rsyslogd    960  962 in:imuxso       root   12w      REG              254,5 493060096        137 /var/log/daemon.log.1 (deleted)
rsyslogd    960  962 in:imuxso       root   13w      REG              254,5  17715200        110 /var/log/messages.1 (deleted)
rsyslogd    960  962 in:imuxso       root   16w      REG              254,5 545968128        342 /var/log/auth.log.1 (deleted)
rsyslogd    960  962 in:imuxso       root   18w      REG              254,5  38313984        341 /var/log/cron.log.1 (deleted)
rsyslogd    960  963 in:imklog       root   12w      REG              254,5 493060096        137 /var/log/daemon.log.1 (deleted)
rsyslogd    960  963 in:imklog       root   13w      REG              254,5  17715200        110 /var/log/messages.1 (deleted)
rsyslogd    960  963 in:imklog       root   16w      REG              254,5 545968128        342 /var/log/auth.log.1 (deleted)
rsyslogd    960  963 in:imklog       root   18w      REG              254,5  38313984        341 /var/log/cron.log.1 (deleted)
rsyslogd    960  964 in:imfile       root   12w      REG              254,5 493060096        137 /var/log/daemon.log.1 (deleted)
rsyslogd    960  964 in:imfile       root   13w      REG              254,5  17715200        110 /var/log/messages.1 (deleted)
rsyslogd    960  964 in:imfile       root   16w      REG              254,5 545968128        342 /var/log/auth.log.1 (deleted)
rsyslogd    960  964 in:imfile       root   18w      REG              254,5  38313984        341 /var/log/cron.log.1 (deleted)
rsyslogd    960  965 in:imudp        root   12w      REG              254,5 493060096        137 /var/log/daemon.log.1 (deleted)
rsyslogd    960  965 in:imudp        root   13w      REG              254,5  17715200        110 /var/log/messages.1 (deleted)
rsyslogd    960  965 in:imudp        root   16w      REG              254,5 545968128        342 /var/log/auth.log.1 (deleted)
rsyslogd    960  965 in:imudp        root   18w      REG              254,5  38313984        341 /var/log/cron.log.1 (deleted)
rsyslogd    960  966 rs:main         root   12w      REG              254,5 493060096        137 /var/log/daemon.log.1 (deleted)
rsyslogd    960  966 rs:main         root   13w      REG              254,5  17715200        110 /var/log/messages.1 (deleted)
rsyslogd    960  966 rs:main         root   16w      REG              254,5 545968128        342 /var/log/auth.log.1 (deleted)
rsyslogd    960  966 rs:main         root   18w      REG              254,5  38313984        341 /var/log/cron.log.1 (deleted)
```

workaround: restarting rsyslog to release the space.
```
systemctl restart rsyslog
```

The root cause is, the following command does not work in 4.15 template
```
root@r-10-VM:~# invoke-rc.d rsyslog rotate
[FAIL] Closing open files: rsyslogd failed!
```

Fix: use `/usr/lib/rsyslog/rsyslog-rotate` instead
```
root@r-10-VM:~# /usr/lib/rsyslog/rsyslog-rotate
root@r-10-VM:~# cat /usr/lib/rsyslog/rsyslog-rotate

if [ -d /run/systemd/system ]; then
    systemctl kill -s HUP rsyslog.service
else
    invoke-rc.d rsyslog rotate > /dev/null
fi

```

Author: ustcweizhou

systemvm/debian/etc/logrotate.d/rsyslog

@@ -6,7 +6,7 @@
 	notifempty
 	compress
 	postrotate
-		/usr/sbin/invoke-rc.d rsyslog rotate > /dev/null
+		/usr/lib/rsyslog/rsyslog-rotate
 	endscript
 }
 
@@ -30,6 +30,6 @@
 	compress
 	sharedscripts
 	postrotate
-		/usr/sbin/invoke-rc.d rsyslog rotate > /dev/null
+		/usr/lib/rsyslog/rsyslog-rotate
 	endscript
 }