Fix backend SSL tests

Due to incorrect SSL certs copying to backend and wrong setting in
maxscale.cnf it was not possible to active backend SSL.
Additionally, one more maxscale restart added to 'sql_queries' test
to reproduce SSL bug in 2.4.1.
Also ssl.cnf tuned in order to reproduce SSL bug

maxscale-system-test/sql_queries.cpp

@@ -111,6 +111,9 @@ int main(int argc, char* argv[])
 
     Test->check_maxscale_alive(0);
 
+    Test->maxscales->restart_maxscale(0);
+    Test->check_maxscale_alive(0);
+
     int rval = Test->global_result;
     delete Test;
     return rval;