bindings: try importing collections.abc first for forward compatibility

bindings: try importing collections.abc first for forward compatibility

Using the babeltrace Python module with Python 3.3-3.8 gives a warning:

/usr/lib/python3/dist-packages/babeltrace/babeltrace.py:811:
DeprecationWarning: Using or importing the ABCs from 'collections'
instead of from 'collections.abc' is deprecated since Python 3.3,
and in 3.9 it will stop working

Therefore, for forward compability (Python 3.9+), try importing it
using the new way first. Otherwise, fall back on the old way.

Signed-off-by: Christophe Bedard <bedard.christophe@gmail.com>
Change-Id: I7f650593a013643b2fb0b77b0d388cf57bc2b765
Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>