Include selector name in debug output

[roncohen]

It would be useful if the debug output included the selector name so you the selector for each log line and you can more easily update your -d filter to include/exclude them:

This:

2017/08/29 09:13:28.898295 server.go:85: DBG Request: URI=/v1/errors, method=POST, content-length=156

would be

2017/08/29 09:13:28.898295 server.go:85: DBG handler Request: URI=/v1/errors, method=POST, content-length=156

if the call was

logp.Debug("handler", "Request...")

Potential alternatives are:

2017/08/29 09:13:28.898295 server.go:85: DBG/handler Request: URI=/v1/errors, method=POST, content-length=156

2017/08/29 09:13:28.898295 server.go:85: DBG:handler Request: URI=/v1/errors, method=POST, content-length=156

[exekias]

+1, linked it with #5000

[andrewkroh]

How about DBG [selector]? I've been using this in Auditbeat (and I think in a few places in Metricbeat).

2017/08/29 09:13:28.898295 server.go:85: DBG [handler] Request: URI=/v1/errors, method=POST, content-length=156

[roncohen]

@andrewkroh I like that 👍