Fix Windows logging to files

[kisunji]

closes #11773

Our logger uses io.MultiWriter which at minimum writes to os.Stdout and optionally to syslog or log file targets.

When Consul is run as a Windows Service, os.Stdout is not available and any writes by the logger fails silently, which inadvertently stopped writes to other targets because of io.MultiWriter's behaviour:

If a listed writer returns an error, that overall write operation stops 
and returns the error; it does not continue down the list.

This PR uses a noErrorWriter wrapper which never returns an error so that even if writes to Stdout fail, writes to syslog and log file are unaffected.

[dnephin]

Nice fix!

UIWriter also strips trailing newlines, I wonder if that might cause other problems.

Would this also work?

type noErrorWriter struct {
    w io.Writer
}

func (w noErrorWriter) Write(p []byte) (n int, err error) {
    n, _ := w.w.Write(p)
    return n, nil
}

Edit: Oh, I just remembered b4b85bd, which did the opposite of this PR to fix a different bug. So I think we should use something like noErrorWriter to prevent re-introducing that bug. ui.Info is not what we want, we just want to drop any errors.

[dnephin]

Nice! Thanks for debugging and fixing this!

[kisunji]

Testing on windows:

[hc-github-team-consul-core]

🍒 If backport labels were added before merging, cherry-picking will start automatically.

To retroactively trigger a backport after merging, add backport labels and re-run https://circleci.com/gh/hashicorp/consul/542579.

[hc-github-team-consul-core]

🍒✅ Cherry pick of commit 08af4f7 onto release/1.11.x succeeded!

[hc-github-team-consul-core]

🍒✅ Cherry pick of commit 08af4f7 onto release/1.10.x succeeded!