LEDGE-228: added close() method to DirectoryParameters and made it
implement AutoCloseable to allow try-with-resources usage for proper
disposal of nested DirContext.
LEDGE-228: trigger reconnection only on CommunitationExcpetion, passing
NameNotFoundException etc to the caller.
LEDGE-228: close old connection explicitly before creating a new one.
LEDGE-228: report NameNotFoundException as service specific
UserUnknownException allowing the caller to react to it, as it is
usunally non-fatal.