Fix some typos in error messages in the build

buildSrc/src/main/groovy/org/elasticsearch/gradle/test/RestTestPlugin.groovy

@@ -39,7 +39,7 @@ public class RestTestPlugin implements Plugin<Project> {
         if (false == REQUIRED_PLUGINS.any {project.pluginManager.hasPlugin(it)}) {
             throw new InvalidUserDataException('elasticsearch.rest-test '
                 + 'requires either elasticsearch.build or '
-                + 'elasticsearch.standalone-test')
+                + 'elasticsearch.standalone-rest-test')
         }
 
         RestIntegTestTask integTest = project.tasks.create('integTest', RestIntegTestTask.class)

buildSrc/src/main/groovy/org/elasticsearch/gradle/test/StandaloneRestTestPlugin.groovy

@@ -40,9 +40,9 @@ public class StandaloneRestTestPlugin implements Plugin<Project> {
     @Override
     public void apply(Project project) {
         if (project.pluginManager.hasPlugin('elasticsearch.build')) {
-            throw new InvalidUserDataException('elasticsearch.standalone-test, '
-                + 'elasticsearch.standalone-test, and elasticsearch.build are '
-                + 'mutually exclusive')
+            throw new InvalidUserDataException('elasticsearch.standalone-test '
+                + 'elasticsearch.standalone-rest-test, and elasticsearch.build '
+                + 'are mutually exclusive')
         }
         project.pluginManager.apply(JavaBasePlugin)
         project.pluginManager.apply(RandomizedTestingPlugin)