python tests: support PEP-3147 installation layout

python tests: support PEP-3147 installation layout

This fixes several spurious testsuite failures with python >= 3.2,
introduced by recent commit v1.12.4-43-ge0e99ed, "python: improve
support for modern python (CPython 3.2 and PyPy)".

* t/ax/am-test-lib.sh (python_has_pep3147, pyc_location, py_installed):
New functions.
($am_pep3147_tag): New variable.
* t/py-compile-basic2.sh: Deleted, too difficult to adapt for the
gain it would offer; move the still relevant parts ...
* t/py-compile-basic.sh: ... here.  Adapt and adjust the rest of
the test as well.
* t/nobase-python.sh: Adapt and adjust.
* t/py-compile-basedir.sh: Likewise.
* t/py-compile-destdir.sh: Likewise.
* t/py-compile-option-terminate.sh: Likewise.
* t/python-pr10995.sh: Likewise.
* t/python-virtualenv.sh: Likewise.
* t/python10.sh: Likewise.
* t/python12.sh: Likewise.
* t/python3.sh: Likewise.
* t/list-of-tests.mk: Adjust list of tests.

Signed-off-by: Stefano Lattarini <stefano.lattarini@gmail.com>