Add is_sort_key for vpnaas attribute maps
Add is_sort_key for vpnaas attribute maps

Add 'is_sort_key' for base vpnaas resources attribute:
vpnservices, ipsec_site_connections, ipsecpolicies, ikepolicies.

Change-Id: Ibd48431aa503f162cbafed6ea783dee2f5779017

openstack/neutron-lib,openstack/neutron-lib,openstack/neutron-lib,openstack/neutron-lib