OF-3035: Propagate session 'detached' state through cluster
This commit ensures that all cluster nodes can see the 'detached' state of a session. Prior to this change, this was only visible at the local cluster node. Because of this, cluster tasks that cannot operate on detached sessions no longer are invoked.
Additionally, certain cluster tasks that cannot succeed on a detached session are now logged in a less verbose manner than on level 'error'.
OF-3036: Improve log message when remote domain is unreachable
This drops the stack trace, and changes the log message in such a way that it's more descriptive to an admin.
OF-3034: Reduce log level for cluster task that can be expected to fail.
The 'removeDetached' cluster task is preemptively fired, and is likely to not find a session to be detached.
As not finding an applicable session is to be expected, this shouldn't be logged as an error.
