Rewrite the logic used to handle Redis commands with clustering.

The reason for this change is to support the upcoming redis-cluster since
it has different behaviors compared to the client-side cluster implementation
provided by Predis. For example redis-cluster will not support key tags or
certain operations currently available with our client-side implementation.

lib/Predis/Command/ConnectionPing.php

@@ -25,14 +25,6 @@ class ConnectionPing extends AbstractCommand
         return 'PING';
     }
 
-    /**
-     * {@inheritdoc}
-     */
-    protected function canBeHashed()
-    {
-        return false;
-    }
-
     /**
      * {@inheritdoc}
      */