Throw a better error message if attempting to access a directory without permission.

Author: childsb

src/main/java/org/apache/hadoop/fs/glusterfs/GlusterVolume.java

@@ -281,6 +281,10 @@ public FileStatus[] listStatus(Path f) throws IOException {
           return new FileStatus[] {
             new GlusterFileStatus(localf, getDefaultBlockSize(), this) };
         }
+        
+        if(localf.isDirectory() && !localf.canRead()){
+            throw new IOException("Access denied.");
+        }
 
         File[] names = localf.listFiles();
         if (names == null) {