neutralinojs-cli test error handling

[yuechenw213]

Hi,
I found that when running npm test for neutralinojs-cli, a folder named testNeuCli would be created. However if the test failed, the folder would keep existing, user need to delete it to run a new test. I suppose keeping the test file may help locate bugs, if not so, maybe it is better to log detailed error message and delete the test folder for future tests convenience.