Move status_url from webapp to web section

The webapp will be fully replaced by zuul-web so also move the
status_url setting there.

Change-Id: I8278d9ca81ed7b0a2a2189d42b8b69c5eea2bab5
diff --git a/etc/zuul.conf-sample b/etc/zuul.conf-sample
index 17092af..3b1ad76 100644
--- a/etc/zuul.conf-sample
+++ b/etc/zuul.conf-sample
@@ -39,11 +39,11 @@
 port=9000
 static_cache_expiry=0
 ;sql_connection_name=mydatabase
+status_url=https://zuul.example.com/status
 
 [webapp]
 listen_address=0.0.0.0
 port=8001
-status_url=https://zuul.example.com/status
 
 [connection gerrit]
 driver=gerrit