Improve error reporting when controller-config mount operation fails

After a new netconf connector config is POSTED, you can't update it via restconf (nor DELETE or GET). With POST you get "data already exists", which makes sense since POST is create-if-not-exists (although this erroneously worked in Helium).

PUT with, eg, the following URL:

http://localhost:8181/restconf/config/network-topology:network-topology/topology/topology-netconf/node/controller-config/yang-ext:mount/config:modules/module/odl-sal-netconf-connector-cfg:sal-netconf-connector/new-netconf-device

should work but fails with error:

"odl-sal-netconf-connector-cfg:sal-netconf-connector from URI can't be resolved. For key which is of type identityref it should be in format module_name:identity_name."

Clearly "odl-sal-netconf-connector-cfg:sal-netconf-connector" is in the correct format.

The problem is in RestCodec.ObjectCodec#deserialize:

if (type instanceof IdentityrefTypeDefinition) {
if (input instanceof IdentityValuesDTO)

{ return identityrefCodec.deserialize(maybeIdentityref); }

logger.debug("Value is not instance of IdentityrefTypeDefinition but is {}. Therefore NULL is used as translation of - {}",
input == null ? "null" : input.getClass(), String.valueOf(input));
return null;
}

It expects the 'input' value to be of type IdentityValuesDTO but it's a String. In fact the calling code in ControllerContext#addKeyValue specifically treats the value as a String. So there's a disconnect between ControllerContext and RestCodec.ObjectCodec. I'm not sure what the intent is here, ie who is supposed to parse the identityref string into an IdentityValuesDTO instance.

I locally changed ObjectCodec#deserialize to check for instanceof String and parse into an IdentityValuesDTO. This fixed the problem.

Note: with this bug no config module can be updated via restconf, including OOB ones.