erp5: stop including -----\n in zope logfiles

This patch change the log format from:

```
2016-03-25 04:26:37,609 WARNING access 172.17.0.2 - Anonymous [25/Mar/2016:04:26:37 +0200] "GET / HTTP/1.0" 200 0 "" ""
------
2016-03-25 04:26:37,613 WARNING access 172.17.0.2 - Anonymous [25/Mar/2016:04:26:37 +0200] "GET / HTTP/1.0" 200 1971 "" ""
------
2016-03-25 04:26:37,619 WARNING access 172.17.0.2 - Anonymous [25/Mar/2016:04:26:37 +0200] "GET / HTTP/1.1" 200 1952 "" ""
------
2016-03-25 04:26:40,619 WARNING access 172.17.0.2 - Anonymous [25/Mar/2016:04:26:40 +0200] "GET / HTTP/1.0" 200 1971 "" ""
------
2016-03-25 04:26:43,622 WARNING access 172.17.0.2 - Anonymous [25/Mar/2016:04:26:43 +0200] "GET / HTTP/1.0" 200 1971 "" ""
```

to something more concise for the eye:


```
2016-04-06 10:13:41,854 WARNING access 172.17.0.2 - Anonymous [06/Apr/2016:10:13:41 +0200] "GET / HTTP/1.0" 200 1971 "" ""
2016-04-06 10:13:44,861 WARNING access 172.17.0.2 - Anonymous [06/Apr/2016:10:13:44 +0200] "GET / HTTP/1.0" 200 1971 "" ""
2016-04-06 10:13:47,868 WARNING access 172.17.0.2 - Anonymous [06/Apr/2016:10:13:47 +0200] "GET / HTTP/1.0" 200 1971 "" ""
2016-04-06 10:13:50,875 WARNING access 172.17.0.2 - Anonymous [06/Apr/2016:10:13:50 +0200] "GET / HTTP/1.0" 200 1971 "" ""
2016-04-06 10:13:53,882 WARNING access 172.17.0.2 - Anonymous [06/Apr/2016:10:13:53 +0200] "GET / HTTP/1.0" 200 1971 "" ""
2016-04-06 10:13:56,890 WARNING access 172.17.0.2 - Anonymous [06/Apr/2016:10:13:56 +0200] "GET / HTTP/1.0" 200 1971 "" ""
```

by changing the log format from the default `------\n%(asctime)s %(levelname)s %(name)s %(message)s` ( defined [here](https://github.com/zopefoundation/ZConfig/blob/0d6a8a1/ZConfig/components/logger/handlers.xml#L38
)) to simply `%(asctime)s %(levelname)s %(name)s %(message)s`

It is enabled for both event.log and Z2.log


/cc @kazuhiko @vpelletier @tc 


/reviewed-on nexedi/slapos!67

stack/erp5/buildout.cfg

@@ -182,7 +182,7 @@ md5sum = 1b515056c5892a86d4ece252ad114a97
 [template-zope-conf]
 <= download-base
 filename = zope.conf.in
-md5sum = c1cd0be406152c79e137dcf8c81f52f2
+md5sum = 77ab4f229a92e02603028a0bd3772edd
 
 [template-runzope-userhosts-preloaded]
 <= download-base

stack/erp5/zope.conf.in

@@ -88,6 +88,7 @@ products {{ parameter_dict['instance-products'] }}
   level WARN
   <logfile>
     dateformat
+    format %(message)s
     path {{ parameter_dict['z2-log'] }}
   </logfile>
 </logger>