use RetriableException to handle retriable connection errors

[elakito]

• Use a subclass of RetriableException for retrievable connection errors so that the source task doesn't terminate when the connection to HANA is lost.
• Remove com.sap.kafka.utils.ConnectorException that was used as the root exception class.
• Reorganize the existing HANAxxxxxxException to retriabled and non-retriable exceptions.
• Use the same approach at the sink task to retry when an retriable exception is thrown.

This provides a solution to #142