GUACAMOLE-1289: Prevent IdentifierGenerator utility class from being instantiated.

guacamole-ext/src/main/java/org/apache/guacamole/net/auth/IdentifierGenerator.java

@@ -36,6 +36,12 @@ public class IdentifierGenerator {
      */
     private static final SecureRandom secureRandom = new SecureRandom();
 
+    /**
+     * IdentifierGenerator is a utility class that is not intended to be
+     * separately instantiated.
+     */
+    private IdentifierGenerator() {}
+    
     /**
      * Generates a unique and unpredictable identifier. Each identifier is at
      * least 256-bit and produced using a cryptographically-secure random