Created by: Haichao-Zhang

Fixing some bugs related to hierarchical-RNN
1) fix a bug in data feeder which returns an LoDTensor with a
   reversed lod structure when lod_level > 1
2) fix a bug in setting lod with the corresponding lod_level
   during array to lod_tensor conversion (in array_to_lod_tensor_op.cc
   and lod_rank_table.cc)
3) some fix in lod_tensor_to_array_op.cc related to getting the correct
   lod_and_offset at different lod_levels
4) some other minor fixes:
    * enable Print to be used within an RNN block
    * add prefix for memory related variables in DynamicRNN