python: AC_PATH_PROG -> AC_PATH_PROGS and fix search order

.. to python26 python2 python as some distros have python == python3

Change-Id: I5fe8bc13546ff9b66571fdb7d9f83a6879e928e6
Merge "python: AC_PATH_PROG -> AC_PATH_PROGS and fix search order" into release_33