Add a 'is_sort_key' keyword for each attribute that can
be used as a sort_key. In the future, we will rely on this keyword
to perform validation: https://review.openstack.org/#/c/554368/ .
This patch processes the following resources: ports, segments,
trunks, address scopes, floating IPs, routers, subnetpools,
subnets, flavors, logging, metering, qos related resources.
Note: This patch only processes the attributes that are documented
as sort_key in api-ref.
Change-Id: I936378855ba43bd7dfdb25a5e324a4bd3e21345d
Related-Bug: #1749820
969cf9ecb8