Report claim and delete latency separately in the benchmark tool

The consumer worker actually performs two different operations. First
it claims a batch of messages, then it deletes each one before getting
the next batch.

Therefore, in order to better compare the latency of enqueuing a message
against other operations, this patch changes the reporting to provide
the individual latency of those other operations.

Change-Id: Iff7f6054904a03dc240d3f7a2a0529bd990f973b
Merge "Report claim and delete latency separately in the benchmark tool"