(PUP-753) Write a JMeter CSV log

This adds a JMeter format CSV log of the benchmark runs. This log will
allow us to track the performance over time via Jenkins and the
Performance plugin.
(PUP-753) Add task to run/profile all scenarios

In order to make it easy to bulk collect the benchmark data there needs
to be a single command to run all of the scenarios. This adds
`benchmark:all:run` and `benchmark:all:profile` to achieve this.
(PUP-753) Write times in millis

The JMeter format is to use milliseconds to express time. This changes
the timestamp and elapsed time to be in millis.
(PUP-753) Benchmark system startup

This adds a simple benchmark to check how long it takes to get puppet to
respond to commands on the CLI. This is an important aspect of percieved
performance for many users. And for anyone trying to script puppet
commands, this becomes a *very* important aspect of actual system
performance.
Merge pull request #2338 from zaphod42/feature/master/pup-753-record-benchmark-times

(PUP-753) Write a JMeter CSV log