Add zuul status url to zuul config.

Zuul can now provide links to the status page if a url for that page is
included in the zuul configuration. Add the status_url option to the
zuul config erb and default it to https://$fqdn/zuul/status.

Change-Id: I160a4e1cd71a13981cb171c71a923cc1af753a80
Reviewed-on: https://review.openstack.org/13859
Reviewed-by: James E. Blair <corvus@inaugust.com>
Reviewed-by: Monty Taylor <mordred@inaugust.com>
Approved: James E. Blair <corvus@inaugust.com>
Tested-by: Jenkins

modules/zuul/manifests/init.pp

@@ -5,6 +5,7 @@ class zuul (
     $gerrit_server,
     $gerrit_user,
     $url_pattern,
+    $status_url="https://${::fqdn}/zuul/status",
     $git_source_repo='https://github.com/openstack-ci/zuul.git'
 ) {
   $packages = ["python-webob",

modules/zuul/templates/zuul.conf.erb

@@ -15,3 +15,4 @@ state_dir=/var/lib/zuul
 git_dir=/var/lib/zuul/git
 push_change_refs=true
 url_pattern=<%= url_pattern %>
+status_url=<%= status_url %>