title: Set smallfiles in ShardingTest
body: <p>I know there is a ShardingTest() object that can be used to create a testing sharding environment (see <a href="https://serverfault.com/questions/590576/installing-multiple-mongodb-versions-on-the-same-server">https://serverfault.com/questions/590576/installing-multiple-mongodb-versions-on-the-same-server</a>), eg:</p>
  
  <pre><code>mongo --nodb
  cluster = new ShardingTest({shards : 3, rs : false})
  </code></pre>
  
  <p>However, given that the disk space in my testing machine is limited and I'm getting "Insufficient free space for journal files" errors when using the above command, I'd like to set the smallfiles option. I have tried with the following with no luck:</p>
  
  <pre><code>cluster = new ShardingTest({shards : 3, rs : false, smallfiles: true})
  </code></pre>
  
  <p>How smallfiles can be enabled for a sharding test, please? Thanks!</p>