【To rel/0.11】Fix modules can not be found when using pypi to pack client-py

[jixuan1989]

In this PR, the client-py package structure will be:
.
├── iotdb
│   ├── Session.py
│   ├── init.py
│   ├── thrift
│   │   ├── init.py
│   │   ├── cluster
│   │   │   ├── RaftService-remote
│   │   │   ├── RaftService.py
│   │   │   ├── TSDataService-remote
│   │   │   ├── TSDataService.py
│   │   │   ├── TSMetaService-remote
│   │   │   ├── TSMetaService.py
│   │   │   ├── init.py
│   │   │   ├── constants.py
│   │   │   └── ttypes.py
│   │   ├── rpc
│   │   │   ├── TSIService-remote
│   │   │   ├── TSIService.py
│   │   │   ├── init.py
│   │   │   ├── constants.py
│   │   │   └── ttypes.py
│   │   └── sync
│   │   ├── SyncService-remote
│   │   ├── SyncService.py
│   │   ├── init.py
│   │   ├── constants.py
│   │   └── ttypes.py
│   └── utils
│   ├── Field.py
│   ├── IoTDBConstants.py
│   ├── IoTDBRpcDataSet.py
│   ├── RowRecord.py
│   ├── SessionDataSet.py
│   ├── Tablet.py
│   └──__init__.py

So, after pip3 install apache-iotdb, just use from iotdb.Session import Session
( and from iotdb.utils import Tablet if you need some advanced APIs).

Thank @JulianFeinauer and @SilverNarcissus 's contribution.

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