Make consoleauth token verification pass an Instance object

The consoleauth manager looks up and passes a SQLite model to the
compute_rpcapi.validate_console_port() method, which is expecting
an Instance object now. This fixes that by replacing the direct call
with an object lookup.

Change-Id: I48a63805e4691899396559f48b29bef3030d5ef8
Merge "Make consoleauth token verification pass an Instance object"