Introduce verbose opcode result for console

With this patch OpConnectConsole will no longer just return a command
with arguments, but rather a detailed description about how to connect
to an instance's console. Unittests for some parts are included. Another
patch will follow to adjust the hypervisor abstractions for the new
model.

Signed-off-by: Michael Hanselmann <hansmi@google.com>
Reviewed-by: Iustin Pop <iustin@google.com>
Reviewed-by: René Nussbaumer <rn@google.com>