Optimize handling of jvmRoute in ClusteredSession ids

The distributed session management logic has too many calls to strip a potential jvmRoute from a session id so the raw id can be used. To clean this up we need to:

1) Only strip the jvmRoute if useJK is true.
2) Wherever possible, strip the jvmRoute once at the edge points of the code, and thereafter pass the stripped id through internal methods. Internal methods should just assume the stripped id has been passed.
3) Maintain the stripped route as a transient property of the session itself. This will make it available to code that has access to the session object, but not to a stripped id.