Handle dead-connection errors for users of python-oracledb

Handle dead-connection errors for users of python-oracledb

The major release of cx_Oracle after 8.3 was renamed python-oracledb.  Until
SQLAlchemy natively supports this namespace, to use python-oracledb instead of
cx_Oracle, user applications can add these lines in the first executed file:

    import sys
    import oracledb
    oracledb.version = "8.3.0"
    sys.modules["cx_Oracle"] = oracledb

This commit checks the new dead-connection error numbers that python-oracledb
generates.