Make "unknown" classloader unique

If we can not obtain the name of the classloader then add the proxies
identityHashCode so they will be unique amongst all others.

src/main/java/hudson/remoting/RemoteClassLoader.java

@@ -44,6 +44,7 @@
 import java.util.HashMap;
 import java.util.HashSet;
 import java.util.List;
+import java.util.Locale;
 import java.util.Map;
 import java.util.Set;
 import java.util.Vector;
@@ -175,7 +176,7 @@ public static ClassLoader create(@CheckForNull ClassLoader parent, @NonNull ICla
         try {
             name = proxy.getName();
         } catch(IOException ignored) {
-            name = "unknown-due-to-io-error";
+            name = String.format(Locale.ROOT, "unknown-due-to-io-error %1$#x", System.identityHashCode(proxy));
         }
         return new RemoteClassLoader(name, parent, proxy);
     }