Fix build when default python is python3

As the python generator scripts are written in python2,
the ./configure script must check for python2 before checking for python
otherwise, on platforms where both python2 and python3 are available and
on which the default python points to python3, ./configure will try to use
the wrong one.
Signed-off-by: NLénaïc Huard <lenaic@lhuard.fr.eu.org>

configure.ac

@@ -2032,7 +2032,7 @@ AM_CONDITIONAL([WITH_HYPERV], [test "$with_hyperv" = "yes"])
 
 
 dnl Allow perl/python overrides
-AC_PATH_PROG([PYTHON], [python])
+AC_PATH_PROGS([PYTHON], [python2 python])
 AC_PATH_PROG([PERL], [perl])
 
 AC_ARG_ENABLE([with-test-suite],