Don't throw exception when user not found

Return a list of missing users, and create VMs for the existing users instead of throwing an exception.

circle/vm/models/instance.py

@@ -442,16 +442,16 @@ class Instance(AclBase, VirtualMachineDescModel, StatusModel, OperatedMixin,
     @classmethod
     def mass_create_for_users(cls, template, users, **kwargs):
         """
-        Create and deploy an instance of a template
-        for each user in a list of users.
+        Create and deploy an instance of a template for each user
+        in a list of users. Returns the user IDs of missing users.
         """
         user_instances = []
-        user_id = None
-        try:
+        missing_users = []
         for user_id in users:
+            try:
                 user_instances.append(User.objects.get(profile__org_id=user_id))
             except User.DoesNotExist:
-            raise Exception("User with id %s doesn't exist" % user_id)
+                missing_users.append(user_id)
 
         instances = []
         for user in user_instances:
@@ -459,7 +459,7 @@ class Instance(AclBase, VirtualMachineDescModel, StatusModel, OperatedMixin,
             instance.deploy(user=user)
             instances.append(instance)
 
-        return instances
+        return missing_users
 
     def clean(self, *args, **kwargs):
         self.time_of_suspend, self.time_of_delete = self.get_renew_times()