bsc: stop all components before terminating testcase

It seems mtc.stop() alone does not really solve the race conditions when
shutting down components. The error happens when messages are sent on
ports which are no longer connected since the receiving component has
terminated.
Some web search
http://www.ttcn-3.org/TTCN3UCAsia2007/Presentations/TTCN3%20UC%202007%20Concurrent%20TTCN.pdf
suggested that one should stop all components before
calling mtc.stop (slide 38). Slide 33 also mentions the difference
between .stop and .kill. Kill removes the port connections while stop
does not. And I think looking at the logs when the testcase teminates
(through mtc.stop or otherwise) it is internally calling kill on all the
components. So hopefully stopping all components and then stopping the mtc
will fix this nasty issue.

I verified locally that the situation improves between commits now when
running BSC_Tests.TC_paging_imsi_nochan_all 20 times in a loop and
otherwise generating load on the system. It reliably failed before this
patch and I wasn't able to get it to fail with it.

Change-Id: I398883492919ceabcf94b5cc2361c63ec772d9d5

bsc/BSC_Tests.ttcn

@@ -114,6 +114,7 @@ modulepar {
 }
 
 private function f_shutdown_helper() runs on test_CT {
+	all component.stop;
 	setverdict(pass);
 	mtc.stop;
 }