Updated openstack/openstack
Project: openstack/nova  53c74ca722a95ad67abe9de7dba8e1c313bded9f

Add read_only field attribute

Some fields of an object are created by the database automatically
like 'id' in service object, thus should not be changed in general.

Add a read_only field attribute to specify such situation, which
can only be set once and can't be changed any more.

Change-Id: I25ba81ed7ec0d16782a59851944a14792d4c84ce