Pass Instance object to spice compute rpc api

Update the get_spice_console() method of the compute rpc api to take in
an Instance object instead of a dict.  The object_compat() decorator is
used to maintain backwards compatibility with receiving a dict.

Change-Id: I0bafe18d9c8bffcd0b72629542fbf7aedacdfbb4
Merge "Pass Instance object to spice compute rpc api"