runnerw: exit with non-zero code if child process cannot be created

Use exit code=2 to emulate "CreateProcess error=2, The system cannot find the file specified"
https://msdn.microsoft.com/en-us/library/windows/desktop/ms681382(v=vs.85).aspx

native/runner/runnerw/runnerw.cpp

@@ -297,7 +297,7 @@ int main(int argc, char * argv[]) {
 		ErrorMessage("CreateProcess");
 		CloseHandle(newstdin);
 		CloseHandle(write_stdin);
-		exit(0);
+		exit(2);
 	}
 	if (hasConsoleWindow || childParams.createNewConsole) {
 		attachChildConsole(pi);