Low: daemons: Get rid of some logged warnings in execd.

handle_ipc_fwd_request and handle_poke_request are pretty obvious.
These two functions need to call pcmkset_result to set the rc value
into the result object or else execd will log a message about "Unknown
status (bug?)". This should have been done as part of #3915 which
converted execd to use pcmkrequest_t.

The other changes in ipc_proxy_forward_client are just to enable setting
the proper rc value for handle_ipc_fwd_request.

handle_rsc_info_request is a little less obvious because ENODEV seems
like something we should definitely be logging. However, this will be
returned as part of regular processing - see the existing comment.
Logging the error ENODEV message is alarming, and before execd used
pcmk__request_t it wasn't treated as an error. So we'll restore that
here.