According to documentation (and personal experience), AM_PATH_PYTHON
selects the highest version of python, no matter if major version is
different, which means if both python2 and 3 are available, 3 will be
chosen an PYTHON will point to "/.../python" which is python3. Apparently,
the macro cannot be easily used to pick highest python2 version.
As {vty,ctrl}_test_runner.py require python2 and are incompatible with
python3, let's instead rely on the system having a "python2" binary
available, which is the case in most distros.
Change-Id: If8e57924ed2c8da7ab7692f58a4bb5c5a970484f
Pau Espin
266b61abc6