Latency measurement

[jage]

• Measure latency by looking at message timestamp leaving lavinmqperf producer, and comparing when it's consumed in lavinmqperf
• Sync producer and consumer start, don't start producing unless there's a consumer running
• Purge queue to ensure there's no old messages in perf queue
• Print measurements in logfmt (lavinmqperf option)

Optional

• Ping during benchmark to get network latency (separate script during benchmark, or in lavinmqperf?)
• Look at how multi threading works in lavinmqperf

[tbroden84]

First iteration of measure latency: #35