Assign code to timeout behavior

While 'timeout' is not something defined in the IPMI spec
(it would make no sense), assign it an impossible value
so that calling code will experience timeout condition
as if it were a 'normal' ipmi error.

Change-Id: I8165497704148b79bc7996229f6f889b011e6d56

pyghmi/ipmi/command.py

@@ -384,7 +384,7 @@ class Command(object):
             if 'error' in rsp:
                 if rsp['code'] == 203:  # Sensor does not exist, optional dev
                     continue
-                raise Exception(rsp['error'])
+                raise exc.IpmiException(rsp['error'], code=rsp['code'])
             yield self._sdr.sensors[sensor].decode_sensor_reading(rsp['data'])
 
     def get_sensor_descriptions(self):

pyghmi/ipmi/private/constants.py

@@ -1174,4 +1174,5 @@ ipmi_completion_codes = {
     0xd5: "Command not supported in present state",
     0xd6: "Cannot execute command because subfunction disabled or unavailable",
     0xff: "Unspecified",
+    0xffff: "Timeout",  # not ipmi, but used internally
 }

pyghmi/ipmi/private/session.py

@@ -1436,7 +1436,7 @@ class Session(object):
         self.nowait = True
         self.timeout += 1
         if self.timeout > self.maxtimeout:
-            response = {'error': 'timeout'}
+            response = {'error': 'timeout', 'code': 0xffff}
             self.ipmicallback(response)
             self.nowait = False
             self._mark_broken()