Plugin should search dynamically ES data path folder from ES config file

Hello,

Performance-analyzer is searching es data path folder in $ES_HOME/data. But some users put es data folder in another path and specified this new path in path.data in es config file. You should get the good path from it, and not get $ES_HOME/data in your code. All users who made the choice to change the path data will face a crash.

Issue on github : https://github.com/opendistro-for-elasticsearch/performance-analyzer/issues/206

Thanks,
Julien Elk