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

          <xsd:attribute name="Command" type="xsd:string" use="optional" default="make -C %(buildpath)s all BEREMIZSRC=%(src)s BEREMIZCFLAGS=%(cflags)s MD5=%(md5)s USE_BEREMIZ=1 FROM_BEREMIZ=1"/>