Feature: fencer: pass full result in replies to requests

Rename stonith_construct_reply() to fenced_construct_reply() for consistency,
make it take a full result as an argument rather than separate arguments for
legacy return code and output, and add the full result to the reply (along with
the legacy return code, for backward compatibility).

This is used for peer query replies and some request replies (including replies
to local clients who requested fencing). Other replies, such as those built by
construct_async_reply(), are not affected by this commit.