Fix build failures

Author: jbaiera

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

@@ -428,8 +428,11 @@ class BuildPlugin implements Plugin<Project>  {
 
             Test integrationTest = project.tasks.create('integrationTest', RestTestRunnerTask.class)
             integrationTest.dependsOn(itestJar)
-            integrationTest.doFirst {
-                integrationTest.systemProperty("es.hadoop.job.jar", itestJar.getArchiveFile().get().asFile.absolutePath)
+
+            itestJar.configure { Jar jar ->
+                integrationTest.doFirst {
+                    integrationTest.systemProperty("es.hadoop.job.jar", jar.getArchiveFile().get().asFile.absolutePath)
+                }
             }
 
             integrationTest.testClassesDirs = project.sourceSets.itest.output.classesDirs