Correct the comment of RequestSpec's network_metadata

The network_metadata won't be persisted inside RequestSpec obj.
https://github.com/openstack/nova/blob/ff0f33cf7e44c5d01f3fb999295eff4508c24a14/nova/objects/request_spec.py#L533

But there is comment said the network_metadata field should be
assigned before creating the RequestSpec obj, that is incorrect
description. This patch removes that comment, also adds some notes
for the fields which isn't persisted in RequestSpec obj.

Change-Id: I0ef451a6bac8f5caa837be62a0c2b335b9ed776b
Closes-Bug: 1834005

nova/compute/api.py

@@ -1037,7 +1037,7 @@ class API(base.Base):
                 req_spec.num_instances = num_instances
 
                 # NOTE(stephenfin): The network_metadata field is not persisted
-                # and is therefore set after 'create' is called.
+                # inside RequestSpec object.
                 if network_metadata:
                     req_spec.network_metadata = network_metadata
 

nova/objects/request_spec.py

@@ -67,6 +67,7 @@ class RequestSpec(base.NovaObject):
         'availability_zone': fields.StringField(nullable=True),
         'flavor': fields.ObjectField('Flavor', nullable=False),
         'num_instances': fields.IntegerField(default=1),
+        # NOTE(alex_xu): This field won't be persisted.
         'ignore_hosts': fields.ListOfStringsField(nullable=True),
         # NOTE(mriedem): In reality, you can only ever have one
         # host in the force_hosts list. The fact this is a list
@@ -76,9 +77,11 @@ class RequestSpec(base.NovaObject):
         # node in the force_nodes list. The fact this is a list
         # is a mistake perpetuated over time.
         'force_nodes': fields.ListOfStringsField(nullable=True),
+        # NOTE(alex_xu): This field won't be persisted.
         'requested_destination': fields.ObjectField('Destination',
                                                     nullable=True,
                                                     default=None),
+        # NOTE(alex_xu): This field won't be persisted.
         'retry': fields.ObjectField('SchedulerRetries', nullable=True),
         'limits': fields.ObjectField('SchedulerLimits', nullable=True),
         'instance_group': fields.ObjectField('InstanceGroup', nullable=True),
@@ -88,6 +91,7 @@ class RequestSpec(base.NovaObject):
         'scheduler_hints': fields.DictOfListOfStringsField(nullable=True),
         'instance_uuid': fields.UUIDField(),
         'security_groups': fields.ObjectField('SecurityGroupList'),
+        # NOTE(alex_xu): This field won't be persisted.
         'network_metadata': fields.ObjectField('NetworkMetadata'),
         'is_bfv': fields.BooleanField(),
         # NOTE(gibi): Eventually we want to store every resource request as
@@ -95,6 +99,7 @@ class RequestSpec(base.NovaObject):
         # resources like vcpu, ram, disk, and flavor.extra_spec based resources
         # are not handled this way. See the Todo in from_components() where
         # requested_resources are set.
+        # NOTE(alex_xu): This field won't be persisted.
         'requested_resources': fields.ListOfObjectsField('RequestGroup',
                                                          nullable=True,
                                                          default=None)