A single invocation of mongoreplay replays the ops twice

> mongoreplay play -p /tmp/mr --report /tmp/report

2016/10/19 13:43:26 Doing playback at 1.00x speed

2016/10/19 13:43:26 Preprocessing file

2016/10/19 13:43:26 Preprocess complete

2016/10/19 13:44:18 8080 ops played back in 51.867065941s seconds over 9 connections

2016/10/19 13:44:18 Doing playback at 1.00x speed

2016/10/19 13:44:18 Preprocessing file

2016/10/19 13:44:18 Preprocess complete

2016/10/19 13:45:10 8080 ops played back in 51.858618534s seconds over 9 connections