Refactor client.py session cookie code. Remove session db access. The original code did a session_db.exists test followed by a session_db.getall. Refactor does a getall and if a KeyError is thrown, handles the error. Most likely the session key will be found so exception handling won't be triggered. Added test case to test the exception code path and minor rearrangement of setup code.

try:
    # Python 3+.
    from xmlrpc import client, server
    server.SimpleXMLRPCDispatcher
except (ImportError, AttributeError):
    # Python 2.
    import xmlrpclib as client  # noqa: F401
    import SimpleXMLRPCServer as server