Add relative_priority scheduler option

Change-Id: Ide901da7bc3068f3aafe3b35a110cc7c2de445b0

manifests/init.pp

@@ -32,6 +32,7 @@ class zuul (
   $zookeeper_hosts = '127.0.0.1:2181',
   $zookeeper_session_timeout = undef,
   $tenant_file_name = 'main.yaml',
+  $relative_priority = false,
   $url_pattern = '',
   $status_url = "https://${::fqdn}/",
   $zuul_status_url = 'http://127.0.0.1:8001',

templates/zuulv3.conf.erb

@@ -28,6 +28,7 @@ ssl_key=/etc/zuul/ssl/server.key
 tenant_config=/etc/zuul/layout/<%= @tenant_file_name %>
 log_config=/etc/zuul/logging.conf
 state_dir=/var/lib/zuul
+relative_priority=<%= @relative_priority %>
 
 [zookeeper]
 hosts=<%= @zookeeper_hosts %>