Fix windows build not finding vncvviewer >3 as entry point is a .bat file

[luigi-calori]

fix python which call that search vncviewer and bump out not finding .bat

[Giuncan]

Right now, the command vncviewer.bat starts a black cmd terminal.

[Giuncan]

The which() function is define in two different files:

• rcm/client/logic/rcm_utils.py
• rcm/utils/executable.py

[luigi-calori]

True, likely they have been implemented in different time, and used in different contexts, likely one is copied from spack.
We should decide for one and use it everywhere

[Giuncan]

Found known bug of subprocess with shell=False: python/cpython#74268