wrong metric for ServerResponseCountByStatusCode view

[rjeczalik]

https://github.com/census-instrumentation/opencensus-go/blob/6ddd4bcc9c808594ec82377ce4323c3f7913be6d/plugin/ochttp/stats.go#L263-L269

The ServerLatency metric seems wrong, since there's no ServerResponseCount metric defined nor used. Given that I guess the view was meant to be ServerRequestCountByStatusCode.

Since server latency by status code feels like not that useful view, I was wondering whether ServerResponseCountByStatusCode should be replaced by ServerRequestCountByStatusCode:

	ServerRequestCountByStatusCode = &view.View{
		Name:        "opencensus.io/http/server/request_count_by_status_code",
		Description: "Server request count by status code",
		TagKeys:     []tag.Key{StatusCode},
		Measure:     ServerRequestCount,
		Aggregation: view.Count(),
	}

[bvwells]

Looks like the same issue as #995...