lib: rename bt_graph_consume() -> bt_graph_run_once()

lib: rename bt_graph_consume() -> bt_graph_run_once()

While bt_graph_run() makes the graph run until the end,
bt_graph_run_once() makes it run a single time, that is, a single sink's
(next in the queue) "consume" operation.

Signed-off-by: Philippe Proulx <eeppeliteloop@gmail.com>
Change-Id: I65dc06c93425d5b5aa1f9e31edf3e22bbeaf77f0
Reviewed-on: https://review.lttng.org/c/babeltrace/+/1818
Tested-by: jenkins <jenkins@lttng.org>
Reviewed-by: Simon Marchi <simon.marchi@efficios.com>