Add padding to input tensor

def pad(attrs, inputs, proto_obj):
    """ Add padding to input tensor"""
    new_attrs = translation_utils._fix_attribute_names(attrs, {'pads'  : 'pad_width',
                                                               'value' : 'constant_value'
                                                              })
    new_attrs['pad_width'] = translation_utils._pad_sequence_fix(new_attrs.get('pad_width'))
    return 'pad', new_attrs, inputs