Support list operation for s3 storage

[jeffwang0516]

• Storage type: s3
• Support operation type=list

Example

<workstage name="main">
      <work name="main" workers="1" runtime="180">
        <operation type="list" ratio="100" config="cprefix=s3bench;containers=c(1);oprefix=" />
      </work>
</workstage>