Add possibility to create report (JMeter dashboard) from multiple csv log files

**piotr.mirek** ([Bug 65656](https://bz.apache.org/bugzilla//show_bug.cgi?id=65656&redirect=false)):
This will eliminate need to run JMeter in distributed node in place of multiple instances of single JMeter instances in cloud environment. This also gives a benefit to have possibility to use JMeter dashboard to get stats for multiple runs in one report, instead merging csv files manually.
In the same time should not require too much effort to update implementation.

OS: Linux