Add a JSON type for nested JSON structures

This will be needed for fields with lists or dicts as values.

Related to blueprint add-node-instance-info

Change-Id: I7b24345c1a5107f10733ab3aa95dea29ac6d280b
Add Node.instance_info field

This is necessary for instance-level info accessed by drivers.

Related to blueprint add-node-instance-info

Change-Id: I4688676767a80ac6f1f3d571f0df4ea78bc756e1