Add 'javadoc' task to CI lifecycle check tasks

buildSrc/reaper/src/main/java/org/elasticsearch/gradle/reaper/Reaper.java

@@ -37,7 +37,7 @@
  * Since how to reap a given service is platform and service dependent, this tool
  * operates on system commands to execute. It takes a single argument, a directory
  * that will contain files with reaping commands. Each line in each file will be
- * executed with {@link Runtime#getRuntime()#exec}.
+ * executed with {@link Runtime#exec(String)}.
  *
  * The main method will wait indefinitely on the parent process (Gradle) by
  * reading from stdin. When Gradle shuts down, whether normally or abruptly, the

buildSrc/src/main/groovy/org/elasticsearch/gradle/BuildPlugin.groovy

@@ -676,6 +676,10 @@ class BuildPlugin implements Plugin<Project> {
              */
             (javadoc.options as CoreJavadocOptions).addBooleanOption('html5', true)
         }
+        // ensure javadoc task is run with 'check'
+        project.pluginManager.withPlugin('lifecycle-base') {
+            project.tasks.getByName(LifecycleBasePlugin.CHECK_TASK_NAME).dependsOn(project.tasks.withType(Javadoc))
+        }
         configureJavadocJar(project)
     }