should be able to expose a specific host for cloustack template registration

[poblin-orange]

As the cpi holds the http server exposing the template, for cloudstack template http pull, it should be possible to configure a specific ip / host for template registration. Currently (v8), this ip also the webdav host ip, used by CPI to push the vhd file (in general, this is the bosh director ip. this ip is often not directly accessible from cloudstack).

We should be able to configure the ip/host given to cloudstack.

example use case:

• cloudstack tenant, with isolated network, snat
• A public ip is allocated and associated with the director. This public ip is accessible from cloudstack iaas
• open firewall and add port forwarding to bosh vm, webdav port 8080 When creating a stemcell, bosh director/cpi extracts the image, pushes it in local webdav. We want for cloudstack register api call to use the public ip, not the local webdav / director ip.

[poblin-orange]

should be solved by #55