Document neutron vpn service properties
Document neutron vpn service properties

This adds descriptions to the properties of:
* OS::Neutron::VPNService
* OS::Neutron::IPsecSiteConnection
* OS::Neutron::IKEPolicy
* OS::Neutron::IPsecPolicy
as well as gettext wrapping for the attributes description

Change-Id: I3312cfbeeccee925e6b06b7ac061be16997bdd34
Closes-Bug: #1224182

takeshineshiro/heat,rh-s/heat,pratikmallya/heat,JioCloud/heat,redhat-openstack/heat,rh-s/heat,citrix-openstack-build/heat,srznew/heat,cwolferh/heat-scratch,miguelgrinberg/heat,pratikmallya/heat,rickerc/heat_audit,rdo-management/heat,maestro-hybrid-cloud/heat,pshchelo/heat,miguelgrinberg/heat,openstack/heat,jasondunsmore/heat,gonzolino/heat,cryptickp/heat,dragorosson/heat,rickerc/heat_audit,dims/heat,steveb/heat,varunarya10/heat,JioCloud/heat,noironetworks/heat,takeshineshiro/heat,ntt-sic/heat,NeCTAR-RC/heat,NeCTAR-RC/heat,cryptickp/heat,citrix-openstack-build/heat,rdo-management/heat,maestro-hybrid-cloud/heat,openstack/heat,redhat-openstack/heat,pshchelo/heat,gonzolino/heat,dims/heat,jasondunsmore/heat,steveb/heat,noironetworks/heat,dragorosson/heat,varunarya10/heat,srznew/heat,cwolferh/heat-scratch,ntt-sic/heat