fix(run): don't overwrite err on reaper.Stop()

[thp-canonical]

PR #380 recently changed the way the reaper is stopped.

If runDaemon() returns an error the defer method overwrites the err return value in err = reaper.Stop(). If err was already set to something else, this will in effect overwrite the non-nil err with either nil (if reaper.Stop() returns nil) or a different error (if reaper.Stop() returns a different error).

Currently (without this PR):

• err == nil on defer method entry, reaper.Stop() returns nil - that's okay (no error)
• err == nil on defer method entry, reaper.Stop() returns non-nil - that's okay (reaper error reported)
• err != nil on defer method entry, reaper.Stop() returns nil - err overwritten, runDaemon errorneously returns success
• err != nil on defer method entry, reaper.Stop() return non-nil - err overwritten, runDaemon returns an error properly, but the real error is overwritten by the reaper error message

With this PR:

• err == nil on defer method entry, reaper.Stop() returns nil - that's okay (no error)
• err == nil on defer method entry, reaper.Stop() returns non-nil - that's okay (reaper error reported)
• err != nil on defer method entry, reaper.Stop() returns nil - err is returned properly
• err != nil on defer method entry, reaper.Stop() return non-nil - err is returned, the error from reaper.Stop() is hidden / ignored

Because this defer method is the first one in the function, it will get called last, so it's the one that will have err set on entry if the function returns a non-nil error.

[thp-canonical]

Instead of ignoring the error from reaper.Stop in the last case, how about we just log the reaper.Stop error in all cases? It's during shutdown in any case, so it doesn't actually matter as things will get cleaned up (though currently reaper.Stop never returns an error). Can we do this?

Sounds reasonable, PR updated - thanks! :)

[benhoyt]

@thp-canonical Looks like you just need to replace %w with %v in the logger call to fix the tests.