Fix for Bug NMS-6564

The SFTP Connection are not closed when an exception is thrown using
3GPP XML Collector.

Conflicts:
	protocols/xml/src/main/java/org/opennms/protocols/xml/collector/AbstractXmlCollectionHandler.java
	protocols/xml/src/main/java/org/opennms/protocols/xml/collector/Sftp3gppXmlCollectionHandler.java