Fix plugins loading conflict in the clustered mode 
When multiple instances in clustered mode boot up at the same time, each instances tries to expand the plugin jar file  at the same time and at the same place. This causes plugin loading error.

diff --git a/ngrinder-controller/src/main/java/org/ngrinder/common/model/Home.java b/ngrinder-controller/src/main/java/org/ngrinder/common/model/Home.java
index a35dd0aa9..588fe4fb9 100644
--- a/ngrinder-controller/src/main/java/org/ngrinder/common/model/Home.java
+++ b/ngrinder-controller/src/main/java/org/ngrinder/common/model/Home.java
@@ -99,15 +99,6 @@ public class Home {
 		return directory;
 	}
 
-	/**
-	 * Get the plugin directory.
-	 *
-	 * @return the plugin directory
-	 */
-	public File getPluginDirectory() {
-		return new File(directory, PATH_PLUGIN);
-	}
-
 	/**
 	 * Copy the given file from given location.
 	 *
@@ -182,7 +173,9 @@ public class Home {
 	 * @return plugin cache directory.
 	 */
 	public File getPluginsCacheDirectory() {
-		return getSubFile(PATH_PLUGIN + "_cache");
+		File cacheDir =  getSubFile(PATH_PLUGIN + "_cache");
+		cacheDir.mkdirs();
+		return cacheDir;
 	}
 
 	/**
diff --git a/ngrinder-controller/src/main/java/org/ngrinder/infra/plugin/extension/NGrinderDefaultPluginManager.java b/ngrinder-controller/src/main/java/org/ngrinder/infra/plugin/extension/NGrinderDefaultPluginManager.java
index 1aeb08f0d..f3af53965 100644
--- a/ngrinder-controller/src/main/java/org/ngrinder/infra/plugin/extension/NGrinderDefaultPluginManager.java
+++ b/ngrinder-controller/src/main/java/org/ngrinder/infra/plugin/extension/NGrinderDefaultPluginManager.java
@@ -30,8 +30,8 @@ public class NGrinderDefaultPluginManager extends DefaultPluginManager {
 
 	@Autowired
 	public NGrinderDefaultPluginManager(Config config, ApplicationContext applicationContext) throws MalformedURLException {
-		super(config.getHome().getPluginsDirectory());
-		super.pluginRepository = new DefaultPluginRepository(pluginsDirectory, new JarFileFilter());
+		super(config.isClustered() ? config.getExHome().getPluginsCacheDirectory() : config.getHome().getPluginsCacheDirectory());
+		super.pluginRepository = new DefaultPluginRepository(config.getHome().getPluginsDirectory(), new JarFileFilter());
 	}
 
 	@Autowired

['ngrinder-controller/src/main/java/org/ngrinder/common/model/Home.java', 'ngrinder-controller/src/main/java/org/ngrinder/infra/plugin/extension/NGrinderDefaultPluginManager.java']