bench: start (NUM_CPUS-1) workers

The master is a worker too so fork off one less worker.

benchmark/http_simple_cluster.js

@@ -2,7 +2,8 @@ var cluster = require('cluster');
 var os = require('os');
 
 if (cluster.isMaster) {
-  for (var i = 0, n = os.cpus().length; i < n; ++i) cluster.fork();
+  console.log('master running on pid %d', process.pid);
+  for (var i = 1, n = os.cpus().length; i < n; ++i) cluster.fork();
 } else {
   require(__dirname + '/http_simple.js');
 }