Add more descriptive errors to blob_test functions

The expected and received value are now both logged when an error
occurs. The execution is also cut short to prevent excessive message
flooding as most of the time all comparisons fail.

maxscale-system-test/blob_test.cpp

@@ -175,9 +175,9 @@ int check_longblob_data(TestConnections* Test, MYSQL * conn, unsigned long chunk
         {
             if (data[y] != y)
             {
-                Test->add_result(1, "Data is wrong!\n");
+                Test->add_result(1, "expected %d, got %d", data[y], y);
+                break;
             }
-            //printf("y = %d \t%lu\tid=%d\tx=%d\n", y, data[y], r_id, r_x);
         }
         row++;
     }