Say that IPMI cannot read an identify state

nodeidentify against an IPMI BMC printed the node name, nothing after it, and
exited 0. A script checking the exit code carries on with an empty value,
which is worse than being turned down.

IPMI can set the identify light and has no command to read it back, so aiohmi
has no get_identify. The empty state was a way of not saying so.

The comment above that branch called identify "read-only", which is the
opposite of the truth.

confluent_server/confluent/plugins/hardwaremanagement/ipmi.py

@@ -1482,8 +1482,13 @@ class IpmiHandler:
                 node=self.node, state=self.inputdata.inputbynode[self.node]))
             return
         elif 'read' == self.op:
-            # ipmi has identify as read-only for now
-            await self.output.put(msg.IdentifyState(node=self.node, state=''))
+            # IPMI can set the identify light but has no command to read it
+            # back, so aiohmi offers no get_identify. This used to answer an
+            # empty state, which nodeidentify prints as the node name and
+            # nothing else, exit 0.
+            await self.output.put(msg.ConfluentNodeError(
+                self.node,
+                'IPMI provides no way to read the identify state'))
             return
 
     async def power(self):