Make mkdir.py work under python3 versions below 3.5 (#8194)
Make mkdir.py work under python3 versions below 3.5 (#8194)

* Make mkdir.py work unter python3 versions below 3.5
Because early versions of python3 did not have the optional arg "exist_ok" for "pathlib.Path(...).mkdir(...)" a build under this versions will abort with an error message.
This PR will modify the python script so that it works even under python 3.4 (and below).
esp8266/Arduino,esp8266/Arduino,sticilface/Arduino,esp8266/Arduino,sticilface/Arduino,sticilface/Arduino,esp8266/Arduino,sticilface/Arduino,sticilface/Arduino,esp8266/Arduino