Fix: shadowed variables

Fix: shadowed variables

This fixes some shadowing of variable across the project, as reported by
the gcc option `-Werror=shadow=local`.

Signed-off-by: Francis Deslauriers <francis.deslauriers@efficios.com>
Change-Id: I93820a4fc14e25ed514c6a05bd30ae4c86216326
Reviewed-on: https://review.lttng.org/c/babeltrace/+/2221
Tested-by: jenkins <jenkins@lttng.org>
Reviewed-by: Simon Marchi <simon.marchi@efficios.com>