lib: use BT_LIB_LOG*_APPEND_CAUSE() where appropriate

lib: use BT_LIB_LOG*_APPEND_CAUSE() where appropriate

Use BT_LIB_LOGE_APPEND_CAUSE() or BT_LIB_LOGW_APPEND_CAUSE() where
appropriate, that is, where a public library function eventually fails
(returns an error status code or `NULL` for a creation function).

Signed-off-by: Philippe Proulx <eeppeliteloop@gmail.com>
Change-Id: I86f8588accfdd7e0c8b69e3977d214d30ccbd67d
Reviewed-on: https://review.lttng.org/c/babeltrace/+/1618
Tested-by: jenkins <jenkins@lttng.org>
Reviewed-by: Francis Deslauriers <francis.deslauriers@efficios.com>
Reviewed-by: Simon Marchi <simon.marchi@efficios.com>