Incorrect exception handling due to poor API of CommandLineRunner

[Hello-zoka]

Extends issue #298
Describe the bug

Method createXmlFromJacoco return non-empty string if test case outputs smth. The reason for this is that CommandLineRunner returns the output of the command line process as a string.

If such outputs contain exception-like output(e.g., stack trace), such execution will be held incorrectly

To Reproduce
Generate a test on a class/method outputting something to the stdout

Expected behavior
If execution is successful return an empty string