Register the worker daemon with systemd

When installing a custom initscript for a worker daemon, reload
systemd so it will pick that up before attempting to start the
service. Wrap it in a conditional check for Ubuntu 16.04 or later,
since earlier releases used upstart as their init instead of
systemd. Make sure the initscript template uses a distinct
"provides" key for each instance of the service as well.

This implementation is copied from the puppet-zuul module.

Change-Id: I4f7db205ac4ae29953757220dc0b9ae026ebbc71

manifests/worker.pp

@@ -96,6 +96,17 @@ if ! defined(File['/var/log/subunit2sql']) {
     ],
   }
 
+  if ($::operatingsystem == 'Ubuntu') and ($::operatingsystemrelease >= '16.04') {
+    # This is a hack to make sure that systemd is aware of the new service
+    # before we attempt to start it.
+    exec { "jenkins-subunit-worker${suffix}-systemd-daemon-reload":
+      command     => '/bin/systemctl daemon-reload',
+      before      => Service["jenkins-subunit-worker${suffix}"],
+      subscribe   => File["/etc/init.d/jenkins-subunit-worker${suffix}"],
+      refreshonly => true,
+    }
+  }
+
   service { "jenkins-subunit-worker${suffix}":
     enable     => true,
     hasrestart => true,

templates/jenkins-subunit-worker.init.erb

@@ -1,6 +1,6 @@
 #! /bin/sh
 ### BEGIN INIT INFO
-# Provides:          jenkins-subunit-worker
+# Provides:          jenkins-subunit-worker<%= suffix %>
 # Required-Start:    $remote_fs $syslog
 # Required-Stop:     $remote_fs $syslog
 # Default-Start:     2 3 4 5