Remove virtual int reply(Message *) from CompletionHook.

Signed-off-by: Matt Benjamin <matt@linuxbox.com>
Wrap more xio msg workflow calls with Connection::sp.

This is not so far preventing faults at full rate.

Also remove mapped connections from the entity map when
torn down.

Also remove reply from CompletionHook implementation
(mixed).

Signed-off-by: Matt Benjamin <matt@linuxbox.com>