babeltrace2: Fix python bindings ptests

babeltrace2: Fix python bindings ptests

The python bindings ptests weren't functional. This patch:

  * Adds a patch to allow the tests to be executed on target standalone
  * Sets a variable to allow the right install path to be passed to setup.py
  * Sets the right paths in the ptest runner script for the python modules
  * Installs the missing data needed to run the tests

Base patch was written by Michael Jeanson, RP then tweaked wording
and formatting and added config to complete the work on all arches.

Signed-off-by: Michael Jeanson <mjeanson@efficios.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>