Send Instance object to validate_console_port

Update the validate_console_port() method of the compute rpc api to take
in an Instance object instead of a dict.  The object_compat() decorator
is used to ensure the change is backwards compatible, and that the code
will still work if it receives an instance in dict format.

Change-Id: Ief8fabc8490315acb41bf85ad421683fea31daf9
Merge "Send Instance object to validate_console_port"