have a 'destroy session' or 'sessionCreateFailed' method

[Jonahss]

We need to unset the sessionID if creating a session fails, so that a new session can be created.

Drivers should surround their 'createSession' in a try/catch and undo their state. They should also call super.destroySession or undoSession or whatever we want to call it. This method should unset the sessionId.

[sebv]

Could do the try/catch in the appium package, and keep the driver simple.