Set JAVA13_HOME (elastic#120)

With this commit we set the environment variable JAVA13_HOME so Rally
can pick it up in order to compile and run with JDK 13.

Author: ebadyano

night_rally/fixtures/ansible/Vagrantfile

@@ -293,6 +293,7 @@ Vagrant.configure(2) do |config|
 
       # To allow building Elasticsearch (nightlies) install the minimum set of java versions required on target nodes
       if node != nodes.first && install_build_requirements
+        node_config.vm.provision "shell", inline: install_java(13)
         node_config.vm.provision "shell", inline: install_java(12)
         node_config.vm.provision "shell", inline: symlink_java_8
       end

night_rally/fixtures/ansible/roles/rally-update/tasks/main.yml

@@ -24,6 +24,7 @@
     JAVA10_HOME: /var/lib/jenkins/.java/java10
     JAVA11_HOME: /var/lib/jenkins/.java/openjdk11
     JAVA12_HOME: /var/lib/jenkins/.java/openjdk12
+    JAVA13_HOME: /var/lib/jenkins/.java/openjdk13
   become: true
   become_user: jenkins
   when: not in_vagrant | default("false") | bool
@@ -36,6 +37,7 @@
     JAVA8_HOME: /usr/lib/jvm/java-8-openjdk-amd64
     JAVA11_HOME: /var/lib/jenkins/.java/openjdk11
     JAVA12_HOME: /var/lib/jenkins/.java/openjdk12
+    JAVA13_HOME: /var/lib/jenkins/.java/openjdk13
   become: true
   become_user: jenkins
   when: in_vagrant | default("false") | bool