Bug 1677 - Parser: ListSchemaNodeBuilder keys needs to be a LinkedHashSet

- changed type of kyes in ListSchemaNodeBuilder

Change-Id: I838d51b76f70f6446169f72407db8da43fb5ee03
Signed-off-by: Ladislav Borak <lborak@cisco.com>
Merge "Bug 1677 - Parser: ListSchemaNodeBuilder keys needs to be a LinkedHashSet"