Zuulv3: move the job dir under /var/lib/zuul

We want to ensure that our jobdir and the git repo cache are
on the same filesystem.  Configure the executors to use a dir
under /var/lib/zuul for the jobdir.  We will mount a new (large)
filesystem at /var/lib/zuul to accomodate both.

Change-Id: I91472fa609274aadcf4945aad44f25014c07b105

manifests/init.pp

@@ -323,6 +323,13 @@ class zuul (
     group  => 'zuul',
   }
 
+  file { '/var/lib/zuul/builds':
+    ensure  => directory,
+    owner   => 'zuul',
+    group   => 'zuul',
+    require => File['/var/lib/zuul'],
+  }
+
   file { '/var/lib/zuul/git':
     ensure  => directory,
     owner   => 'zuul',

templates/zuulv3.conf.erb

@@ -48,6 +48,7 @@ git_user_name=<%= @git_name %>
 
 [executor]
 log_config=/etc/zuul/executor-logging.conf
+job_dir=/var/lib/zuul/builds
 <% if @site_variables_yaml_file != nil -%>
 variables=/etc/zuul/site-variables.yaml
 <% end -%>