build, win: vcbuild improvements

Removes extra erroor messages when Python is not installed. Removes
"vswhere not found" message when no VS2017 installation is found.
Adds support for DEBUG_HELPER to vcbuild.bat.

Fixes: nodejs#16864

tools/msvs/find_python.cmd

@@ -19,7 +19,7 @@ EXIT /B 1
 :: Helper subroutine to handle quotes in %1
 :find-main-branch
 SET main_key="%~1\Python\PythonCore"
-REG QUERY %main_key% /s | findstr "2." | findstr InstallPath > NUL 2> NUL
+REG QUERY %main_key% /s 2> NUL | findstr "2." | findstr InstallPath > NUL 2> NUL
 IF NOT ERRORLEVEL 1 CALL :find-key %main_key%
 EXIT /B
 

tools/msvs/vswhere_usability_wrapper.cmd

@@ -28,5 +28,4 @@ for /f "usebackq tokens=*" %%i in (`vswhere %VSWHERE_ARGS%`) do (
 
 :no-vswhere
 endlocal
-echo could not find "vswhere"
 exit /B 1

vcbuild.bat

@@ -1,4 +1,4 @@
-@echo off
+@if not defined DEBUG_HELPER @ECHO OFF
 
 cd %~dp0
 
@@ -165,8 +165,9 @@ if "%target%"=="Clean" echo deleting %~dp0deps\icu
 if "%target%"=="Clean" rmdir /S /Q %~dp0deps\icu
 :no-depsicu
 
-call tools\msvs\find_python.cmd
-if errorlevel 1 echo Could not find python2 & goto :exit
+echo Looking for Python 2.x
+call tools\msvs\find_python.cmd > NUL 2> NUL
+if errorlevel 1 echo Could not find Python installation & goto :exit
 
 call :getnodeversion || exit /b 1