* DAP-20916 - SSH Connections Remain Open After Import Job Completes

* remove session cache from jsch runner and replace by only storing the created session
* do not allow any longer to change connection parameters if the current session is connected
* create always a new session in case the cached session is not set or already closed
* only create debug messages in case debug is enabled
* do not let the cache expiry because we expect a defined life time and want people to explicitly disconnect