OAK-2031: MemoryNodeBuilder#set only works on root builders
Test case

git-svn-id: https://svn.apache.org/repos/asf/jackrabbit/oak/trunk@1621123 13f79535-47bb-0310-9956-ffa450edef68
OAK-2031: MemoryNodeBuilder#set only works on root builders
Delegate to parent.setChildNode for non root builders

git-svn-id: https://svn.apache.org/repos/asf/jackrabbit/oak/trunk@1621124 13f79535-47bb-0310-9956-ffa450edef68