Python not found during configure

[jgraciahlrs]

Our system does not provide the command python, only python2 and python3. I believe this is becoming increasingly widespread.

The configure scripts accepts only python and I do not see a way to change this via options or environment variables.

I suggest to replace

AC_CHECK_PROG(HAVE_PYTHON,[python],[python],[no])

with

AC_CHECK_PROGS(HAVE_PYTHON,[python, python3, python2],[no])

Consider dropping support for python2.

[wujialong163]

No python can be found after modification

[2397798540]

use python2