scaling_policy and software_development signal url conflict

[jz]

In the resource software_deveolpment and scaling_policy,
they obtain the signal url by calling the signal_responder.get_heat_signal_url
or signal_responder.get_ec2_signed_url respectively. The result can only has public_vip or internal_vip.
But in the case when the controller node has no access to public_vip and the vms
created have only access to public_vip. Then there is a conflict. either the software_development
or the scaling_policy can not work.

[jz (danielradcliffe2004)]

I am using the mitaka version

[jz (danielradcliffe2004)]

For security design, heat can only has access to internal_vip, but vms has no access to public_vip