Support generating csv when only collect test cases

[taget]

Would like to only collect cases (not running them) and generage a csv file.

pytest --collect-only -q --csv xx.csv tests/cvm/test_CreateCVM.py::CreateCVM::test_create tests/cvm/test_CreateCVM.py::CreateCVM::test_destroy tests/cvm/test_CreateCVM.py::CreateCVM::test_instance_alive tests/cvm/test_CreateCVM.py::CreateCVM::test_stop_start

[lookilooki]

I would like to have the same functionality.