guest subscriptions have incorrect link to hypervisor
When a subscription type is of the form "Guests of hypervisor-name", the hypervisor-name is a link to the hypervisor itself. The link is broken since it is still including they candlepin uuid rather than the host id.
The subscriptions UI pages on other pages (content host and activation keys) are also broken and need fixing.
When attaching a VDC subscription to a physical host, a link appears
for the guest subscription, "Guests of foo.example.com" This link is
broken as it is still using the candlepin id instead of the active
record id. This commit changes the link to use the proper id, and also
changes the JSON returned. All places in the UI that are using a
subscription's host id should be updated.