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/mxs1677_temp_table.cpp

@@ -13,6 +13,6 @@ int main(int argc, char** argv)
     test.try_query(test.maxscales->conn_rwsplit[0], "CREATE TEMPORARY TABLE test.temp(id INT)");
     test.maxscales->disconnect();
 
-    test.check_log_err(0, "The provided buffer does not contain a COM_QUERY, but a COM_QUIT", false);
+    test.log_excludes(0, "The provided buffer does not contain a COM_QUERY, but a COM_QUIT");
     return test.global_result;
 }