bt2: rename exception handling functions

It's currently not very clear if the Python exception handling functions
append a Babeltrace error cause or clear the Python error indicator.
It's therefore easy to mis-use them.

Rename them to better indicate what they do.

Change-Id: I7dc31264196c6410e715c620cf9e4cd48a2711f6
Signed-off-by: Simon Marchi <simon.marchi@efficios.com>
Reviewed-on: https://review.lttng.org/c/babeltrace/+/2222
Tested-by: jenkins <jenkins@lttng.org>
Reviewed-by: Francis Deslauriers <francis.deslauriers@efficios.com>