Adding instance support to the canary backend.

Now lists, return available hosts and instances. To perform info
or query commands, simply use host:instance_id as the id in the
URL string. The reason we still require hosts is that (for example
with migration) multiple hosts could have the data for the same
instance.

Change-Id: I33fb0265da617c26be5fba2121897b429d12c1ba
Merge "Adding instance support to the canary backend."