*: new --log-prefix flag / option

[ploxiln]

instantiate Logger in nsqd.New() instead of nsqd.NewOptions(), only if not already present in opts

More options spam, I understand if it's not desired. But if you don't mind this, I'll do this for nsqlookupd and nsqadmin as well.

(why? it's redundant with the service / container name in my setup. not a big deal)

[mreiferson]

OK, fine with me, but we should add it for all 3 binaries?

[ploxiln]

That's my suggestion, do it for all three - was just testing the waters with one easier-to-review piece first. I'll add changes for the other two shortly ...

[ploxiln]

Done for nsqd, nsqlookupd, nsqadmin.

I just realized, previously one would be able to set Logger to nil in options to disable logging, now that won't work, you'll have to create a no-op Logger. All these apps have logf() like:

func (n *NSQD) logf(f string, args ...interface{}) {
	if n.getOpts().Logger == nil {
		return
	}
	n.getOpts().Logger.Output(2, fmt.Sprintf(f, args...))
}

(On the upside, we can get rid of that conditional now...)

[ploxiln]

squashed in removal of the now (unfortunately) useless nil checks in logf()