Add bt_graph_add_simple_sink_component() tests

Add bt_graph_add_simple_sink_component() tests

As of this patch, the tests are basic and only check that the statuses
returned by the user functions are correctly translated and returned by
bt_graph_run_once(). The user initialization function status is not
returned by bt_graph_add_simple_sink_component() because the
initialization function is called within the sink component's "graph is
configured" method.

Signed-off-by: Philippe Proulx <eeppeliteloop@gmail.com>
Change-Id: Id8ccfd7df4e4a8f0a39af386ed4ad13fe657f86a
Reviewed-on: https://review.lttng.org/c/babeltrace/+/1830
Reviewed-by: Simon Marchi <simon.marchi@efficios.com>
Reviewed-by: Francis Deslauriers <francis.deslauriers@efficios.com>