Jenkins master: install openjdk-8-jdk-headless (#16955)

Without this package, after Puppet has upgraded Jenkins and its plugins,
I see:

  Error: /Stage[main]/Jenkins::Cli/Exec[jenkins-cli]: Failed to call refresh: Could not find command 'jar'
  Error: /Stage[main]/Jenkins::Cli/Exec[jenkins-cli]: Could not find command 'jar'

manifests/jenkins/master.pp

@@ -57,6 +57,11 @@ class tails::jenkins::master (
     ],
   }
 
+  # Provides the jar command, which is used by Jenkins::Cli/Exec[jenkins-cli]
+  package { 'openjdk-8-jdk-headless':
+    ensure => installed,
+  }
+
   # apt-cacher-ng does not support HTTPS repositories
   apt::conf { 'proxy_jenkins_repo':
     content  => 'Acquire::HTTP::Proxy::pkg.jenkins.io "DIRECT";',