fsm_test: terminate the main loop instead of exit on timeout

In fsm_test.c, we have FSM instance cleanup after the select main loop, but we
exit(0) in the timer cb; hence the final code is never called.

Rather clean up the instance and hence also test that, by using a global flag
to exit the main loop upon timeout.

Adjust expected stderr output.

BTW, in a subsequent commit, I want to move the fsm instance id testing to
below the main loop, to more clearly group the tested bits.

Change-Id: Ia47811ffcc1bd68d2630c86be7ab98fc1f338773
diff --git a/tests/fsm/fsm_test.c b/tests/fsm/fsm_test.c
index d7b08ae..ef7bfe3 100644
--- a/tests/fsm/fsm_test.c
+++ b/tests/fsm/fsm_test.c
@@ -60,13 +60,17 @@
 	}
 }
 
+static bool main_loop_run = true;
+
 static int test_fsm_tmr_cb(struct osmo_fsm_inst *fi)
 {
 	OSMO_ASSERT(fi->T == 2342);
 	OSMO_ASSERT(fi->state == ST_TWO);
 	LOGP(DMAIN, LOGL_INFO, "Timer\n");
 
-	exit(0);
+	main_loop_run = false;
+
+	return 0;
 }
 
 static struct osmo_fsm_state test_fsm_states[] = {
@@ -201,7 +205,7 @@
 	OSMO_ASSERT(osmo_fsm_inst_find_by_name(&fsm, "Test_FSM(another_id)") == finst);
 	OSMO_ASSERT(osmo_fsm_inst_update_id(finst, "my_id") == 0);
 
-	while (1) {
+	while (main_loop_run) {
 		osmo_select_main(0);
 	}
 	osmo_fsm_inst_free(finst);