Don't query database with an empty list for IN clause

Fixes bug 931687

Change-Id: Ieec2c43c1d56c8d54d5bce606db9909b2ef5d6d4

nova/api/openstack/compute/contrib/disk_config.py

@@ -106,6 +106,8 @@ def _add_disk_config(self, context, servers):
         # Filter out any servers that already have the key set
         # (most likely from a remote zone)
         servers = [s for s in servers if API_DISK_CONFIG not in s]
+        if not servers:
+            return
 
         # Get DB information for servers
         uuids = [server['id'] for server in servers]

nova/api/openstack/compute/contrib/extended_status.py

@@ -36,6 +36,9 @@ def __init__(self, *args, **kwargs):
         self.compute_api = compute.API()
 
     def _get_instances(self, context, instance_uuids):
+        if not instance_uuids:
+            return {}
+
         filters = {'uuid': instance_uuids}
         instances = self.compute_api.get_all(context, filters)
         return dict((instance['uuid'], instance) for instance in instances)

nova/compute/api.py

@@ -1731,6 +1731,9 @@ def update_instance_metadata(self, context, instance,
     def get_instance_faults(self, context, instances):
         """Get all faults for a list of instance uuids."""
 
+        if not instances:
+            return {}
+
         for instance in instances:
             check_policy(context, 'get_instance_faults', instance)