Reduce likelihood of indefinite wait in viewer integration tests.

Introduce LLStartupListener to allow viewerclient-based test script to query
startup state. This handles the scenario in which, by the time the test script
manages to connect, the viewer already IS in STATE_STARTED.
Fix ViewerSession to invoke that query before waiting for STATE_STARTED. Make
that wait time out eventually to deal with "System currently logging you off,
please wait 5 minutes." Timeout raises new ViewerWontLogin exception.
Fix testlangs to catch ViewerWontLogin and retry a limited number of times.