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/readconnrouter_master.cpp

@@ -80,7 +80,7 @@ int main(int argc, char* argv[])
     printf("Changing master back to node 0\n");
     Test->repl->change_master(0, 1);
 
-    Test->check_log_err(0, (char*) "The service 'CLI' is missing a definition of the servers", false);
+    Test->log_excludes(0, "The service 'CLI' is missing a definition of the servers");
 
     int rval = Test->global_result;
     delete Test;