sharding: Make nginx shard map owned by zulip:zulip.

This will make it easier to manipulate in restart-server.

puppet/zulip/manifests/tornado_sharding.pp

@@ -7,8 +7,8 @@ class zulip::tornado_sharding {
   # the sharding script afterwards and Puppet shouldn't overwrite them.
   file { '/etc/zulip/nginx_sharding_map.conf':
     ensure  => file,
-    owner   => 'root',
-    group   => 'root',
+    owner   => 'zulip',
+    group   => 'zulip',
     mode    => '0644',
     notify  => Service['nginx'],
     content => @(EOT),