Currently the JSON conversion in Rapi and Luxi are giving something
like:
  Error: failed to load data. Details:
  Unable to read Double

This doesn't tell one where the error is (in a node specification? and
which node? etc.). This patch annotates such messages with the owner
node:
  Error: failed to load data. Details:
  Node 'node1' key 'mtotal': Unable to read Double

For errors during parsing of the node/instance name (unlikely, but
still), the output is:
  Error: failed to load data. Details:
  Parsing new node key 'name': Unable to read String