Exclude 'server' tag from metrics

The tag is equal to the address of the server which is quite useless
when using a Unix socket address.

Change-Id: Ia87c30f8ff2176f923982d70b712b10ec6e97f56
Depends-On: I538dbb24602a8ad4aece0a74445db47810099bb9

galera/meta/telegraf.yml

@@ -15,4 +15,5 @@ agent:
       address: {{ server.socket }}
       username: {{ server.admin.user }}
       password: {{ server.admin.password }}
+      tagexclude: [server]
 {%- endif %}