Transport Client: fixed the node retry mechanism which could fail without trying all the connected nodes

The RetryListener was notified twice for each single failure, which caused some additional retries, but more importantly was making the client reach the maximum number of retries (number of connected nodes) too quickly, meanwhile ongoing retries which could succeed were not completed yet.

The TransportService used to throw ConnectTransportException due to throwConnectException set to true, and also notify the listener of any exception received from a separate thread through the request holder.

Simplified exception handling by just removing the throwConnectException option from the TransportService, used only in the transport client. The transport client now relies solely on the request holder to notify of failures and eventually retry.

Closes #6829