fix: use configured python when building the examples

fix: use configured python when building the examples

Prior to the refactoring of the autotools setup we used different python
detection mechanisms for the python agent feature and the example code.
The example code detection was flawed as it would only work with a
python binary named exactly 'python'. Wire the detected python binary in
the examples Makefile integration.

Change-Id: I07b9222a8869ff154073e5b72fb2ac0d70f14896
Signed-off-by: Michael Jeanson <mjeanson@efficios.com>
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>