Set server admin var so that vhost works

Using the puppet 4 future parser it is far more particular about
variables and their scoping. We don't set a serveradmin in this class
but then attempt to use it in the vhost template. This was fine under
puppet 3 as it would just look for this out of the current scope but
breaks under puppet 4.

Make this trivially happy on puppet 4 by setting a default that is sane.

Change-Id: Id415056cdfa693fd199e0b4a0c6b09e20faf23ef

manifests/js.pp

@@ -23,6 +23,7 @@ class kibana::js (
   $vhost_proxy_connect_timeout = '15',
   $vhost_proxy_timeout         = '120',
   $vhost_template              = 'kibana/dual-elasticsearch.vhost.erb',
+  $serveradmin                 = "webmaster@${::fqdn}",
 ) {
 
   $base_path = "/opt/kibana/${git_revision}"