Switch messy watcher+groovy tests to messy-test plugin

Original commit: elastic/x-pack-elasticsearch@8163f0f129

elasticsearch/qa/messy-test-watcher-with-groovy/build.gradle

@@ -4,18 +4,9 @@
  * https://github.com/elastic/x-plugins/issues/724
  */
 
-apply plugin: 'elasticsearch.standalone-test'
+apply plugin: 'elasticsearch.messy-test'
 
 dependencies {
   testCompile project(path: ':x-plugins:elasticsearch:x-pack', configuration: 'testArtifacts')
   testCompile project(path: ':modules:lang-groovy', configuration: 'runtime')
 }
-
-gradle.projectsEvaluated {
-  Project groovy = project(':modules:lang-groovy')
-  sourceSets.test.resources {
-    srcDir groovy.pluginProperties.generatedResourcesDir
-    srcDir new File(groovy.projectDir, 'src/main/plugin-metadata')
-  }
-  test.dependsOn groovy.pluginProperties
-}