Replace check_log_err with log_includes/log_excludes

The latter are more explicit and easier to understand at the call site.

Also removed the redundant crash checks via the log files.

maxscale-system-test/pers_02.cpp

@@ -39,7 +39,6 @@ int main(int argc, char* argv[])
     Test->add_result(Test->create_connections(0, 70, true, true, true, true),
                      "Connections creation error \n");
 
-    Test->check_log_err(0, (char*) "fatal signal 11", false);
     Test->check_maxscale_alive(0);
     int rval = Test->global_result;
     delete Test;