change the condition to find python interpreter to avoid skipping the find process. (#43888)
change the condition to find python interpreter to avoid skipping the find process. (#43888)

* change to condition to find python interpreter to avoid skipping the find process.
PYTHONINTERP_FOUND is the best signal that python interpreter is found.
PaddlePaddle/Paddle,luotao1/Paddle,PaddlePaddle/Paddle,luotao1/Paddle,PaddlePaddle/Paddle,PaddlePaddle/Paddle,PaddlePaddle/Paddle,PaddlePaddle/Paddle,luotao1/Paddle,luotao1/Paddle,PaddlePaddle/Paddle,luotao1/Paddle,luotao1/Paddle,luotao1/Paddle