fix test_bi_grumemory.protostr, test_recursive_topology.protostr, util_layers.protostr and new test_sub_nested_seq_select_layer.protostr

2. Add crop layer unitest
3. Fix bugs

* Fix  #2797
* It because trainer_config_helpers' __dfs_travel__ did not record the
  node which travelled, and if the topology has a recursive dependency,
  there are some nodes will be travelled multiple times.
* Add a `travelled` set to record which node is travelled.
* Also add a unittest for this situation.

For example:
layer.printer(input=[x, y], format="x=%s y=%s")