rewrite usage setup part for escaping "Error: ENOTEMPTY: directory not empty, rmdir" and "Error: Could not find job" errors

[VitaliLebedzeu]

It should fix the Issue #17 and the "Error: Could not find a job" errors. They come across with putting the "wdioParallel.performSetup()" method as a global function into the "wdio.config.js" because this file is running with each new browser instance. This MR suggests to use the "wdioParallel.performSetup()" method only once in the onPrepare() hook.