return process memory usage in GET CACHE STATS RPC

lib/commands/admin-rpc.js

@@ -50,6 +50,7 @@ var getCacheStats = function (env, server, cb) {
         metaSize: metaSize,
         channel: channelCount,
         channelSize: channelSize,
+        memoryUsage: process.memoryUsage(),
     });
 };