use the current venv to launch therock build

[lamikr]

• use the currently used python venv to launch the therock build from the rockbuilder_cfg.py
• This ensures that rockbuilder_cfg has all the python packages installed that the init_rcb_env.sh/bat installs.
• This fixes a following error detetected on windows where the build tried to use different python env which did not have the windows-curses installed.

Traceback (most recent call last):
File "c:\rock\rockbuilder\rockbuilder.py", line 11
in <module> import rockbuilder_cfg as rcb_cfg_writer File "c:\rock\rockbuilder\rockbuilder_cfg.py", 
line 7, in <module> import curses File "C:\Python313\Lib\curses\__init__.py", line 13, in 
<module> from _curses import * ModuleNotFoundError: No module named '_curses'