python: do not use hg or svn when available

python: do not use hg or svn when available

During the execution of its configure script, Python tries to find an
available "hg" and "svn" installation, and if available, will try to use
them to get information from the version control system. To do this, it
tries to communicate over the network, potentially over ports that are
blocked, causing the build to halt. This was reported by a user as part
of bug #7802.

To solve this, we simply make the Python script use /bin/false as the
"hg" and "svn" programs.

Fixes bug #7802 for the python package.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>