[#493] Refactor serving of prometheus and pprof services

Rename `util/profiler` package to `httputil` and refactor it:

  * simplify utility HTTP server;

  * make more generic server's parameters in order to remove `viper.Viper`
    dependency;

  * use single constructor for creating the pprof and prometheus servers;

  * replace `enabled` config value with empty-check of the network address.

Signed-off-by: Leonard Lyubich <leonard@nspcc.ru>

cmd/neofs-node/metrics.go

@@ -1,17 +1,40 @@
 package main
 
 import (
-	"github.com/nspcc-dev/neofs-node/pkg/util/profiler"
+	"context"
+
+	httputil "github.com/nspcc-dev/neofs-node/pkg/util/http"
+	"github.com/prometheus/client_golang/prometheus/promhttp"
+	"go.uber.org/zap"
 )
 
 func initMetrics(c *cfg) {
-	if c.metricsCollector != nil {
-		c.metricsServer = profiler.NewMetrics(c.log, c.viper)
+	addr := c.viper.GetString(cfgMetricsAddr)
+	if addr == "" {
+		return
 	}
-}
 
-func serveMetrics(c *cfg) {
-	if c.metricsServer != nil {
-		c.metricsServer.Start(c.ctx)
-	}
+	var prm httputil.Prm
+
+	prm.Address = addr
+	prm.Handler = promhttp.Handler()
+
+	srv := httputil.New(prm,
+		httputil.WithShutdownTimeout(
+			c.viper.GetDuration(cfgMetricsShutdownTimeout),
+		),
+	)
+
+	c.workers = append(c.workers, newWorkerFromFunc(func(context.Context) {
+		fatalOnErr(srv.Serve())
+	}))
+
+	c.closers = append(c.closers, func() {
+		err := srv.Shutdown()
+		if err != nil {
+			c.log.Debug("could not shutdown metrics server",
+				zap.String("error", err.Error()),
+			)
+		}
+	})
 }