Fix logging message with async rpc calls.

In case of error.

ccnode/hypervisor/__init__.py

@@ -76,7 +76,8 @@ class Handler(HostHandler):
     def register_domain_cb(self, call_id, response=None, error=None):
         name = self.async_calls.pop(call_id)
         if error is not None:
-            logger.error('Error while registering domain, %s', error)
+            logger.error('Error while registering domain, %s("%s")',
+                         error['exception'], error['message'])
             return
 
         logger.debug('Registered domain %s', name)
@@ -242,7 +243,8 @@ class Hypervisor(object):
     def register_cb(self, call_id, response=None, error=None):
         vm = self.domains[self.async_calls.pop(call_id)]
         if error is not None:
-            logger.error('Error while registering domain to server, %s', error)
+            logger.error('Error while registering domain to server, %s("%s")',
+                         error['exception'], error['message'])
         logger.info('Add domain: %s (%s)', vm.name, vm.uuid)
         # add tags
         for tag in vm.tags.itervalues():
@@ -251,7 +253,8 @@ class Hypervisor(object):
     def unregister_cb(self, call_id, response=None, error=None):
         vm_name = self.async_calls.pop(call_id)
         if error is not None:
-            logger.error('Error while unregistering domain to server, %s', error)
+            logger.error('Error while unregistering domain to server, %s("%s")',
+                         error['exception'], error['message'])
         logger.info('Delete domain: %s', vm_name)
         self.main.remove_sub_object(vm_name)