Replace md5 module with hashlib

fix following pylint error:

************* Module connectors.ConnectorBase
connectors/ConnectorBase.py:7: [W1648(bad-python3-import), ] Module moved in Python 3
************* Module runtime.PLCObject
runtime/PLCObject.py:33: [W1648(bad-python3-import), ] Module moved in Python 3

# -*- coding: utf-8 -*-

# See COPYING.Runtime file for copyrights details.


def _(x):
    """No translation"""
    return x


Broken = _("Broken")
Started = _("Started")
Stopped = _("Stopped")
Disconnected = _("Disconnected")
Empty = _("Empty")