Replace deprecated with_lockmode with with_for_update

The Query.with_lockmode() method is deprecated since version 0.9.0
and will be removed in a future release. [1]
This patch replaces it with Query.with_for_update().

[1] https://docs.sqlalchemy.org/en/13/orm/query.html#sqlalchemy.orm.query.Query.with_lockmode

Change-Id: I78e692e08440afc38ac2697fabfa566fff5f0a9f

Author: madhuri-rai07

nova/db/sqlalchemy/api.py

@@ -1148,7 +1148,7 @@ def floating_ip_update(context, address, values):
 def dnsdomain_get(context, fqdomain):
     return model_query(context, models.DNSDomain, read_deleted="no").\
                filter_by(domain=fqdomain).\
-               with_lockmode('update').\
+               with_for_update().\
                first()
 
 
@@ -3101,7 +3101,7 @@ def network_query(project_filter, id=None):
             filter_kwargs['id'] = id
         return model_query(context, models.Network, read_deleted="no").\
                        filter_by(**filter_kwargs).\
-                       with_lockmode('update').\
+                       with_for_update().\
                        first()
 
     if not force: