fix(tools): honor IDF_PYTHON_ENV_PATH value

The active.py script is currently clearing the IDF_PYTHON_ENV_PATH,
preventing it from being set to a custom location for the python virtual
environment directory. Although the install script checks to ensure that
an existing python virtual environment is not overwritten with one for a
different ESP-IDF version than it was originally created for, we should
still permit setting a custom path for the python virtual environment.

Closes espressif#15006

Signed-off-by: Frantisek Hrbata <frantisek.hrbata@espressif.com>

Author: fhrbata

tools/activate.py

@@ -44,6 +44,6 @@ def die(msg: str) -> None:
 
 try:
     run([virtualenv_python, os.path.join(idf_path, 'tools', 'export_utils', 'activate_venv.py')] + sys.argv[1:], check=True, env=os.environ.copy())
-except (OSError, SubprocessError):
-    die('\n'.join(['Activation script failed',
+except (OSError, SubprocessError) as e:
+    die('\n'.join(['Activation script failed', str(e),
                    'To view detailed debug information, set ESP_IDF_EXPORT_DEBUG=1 and run the export script again.']))