Refactor: fencer: pass full result of previous failed action when initiating peer fencing

Rename call_remote_stonith() to request_peer_fencing() for readability, and
make it take the full result of the previous failed action, rather than just
its legacy return code, as an argument.

This does cause one change in behavior: if topology is in use, a previous
attempt failed, and no more peers have the appropriate device, then the
legacy return code returned will be -ENODEV rather than -EHOSTUNREACH.
These are treated similarly internally, and hopefully that will not cause
problems for external code.