BaseTools: Reset ERRORLEVEL in toolsetup.bat after edk2basetools check

BaseTools: Reset ERRORLEVEL in toolsetup.bat after edk2basetools check

When using the in-source BaseTools, edksetup.bat will exit with an
ERRORLEVEL of 1 because the line in toolsetup.bat
"%PYTHON_COMMAND% -c "import edk2basetools" >NUL 2>NUL"
fails.

Ensure ERRORLEVEL is set to 0 when edksetup.bat or toolsetup.bat is
successfully run.

Signed-off-by: Rebecca Cran <rebecca@bsdio.com>
Reviewed-by: Bob Feng <bob.c.feng@intel.com>
Reviewed-by: Liming Gao <gaoliming@byosoft.com.cn>