daemon: avoid math/rand race by using global source

Unless we're using the global source for math/rand, (*rand.Rand).Read
should not be called concurrently. We seed the rng in daemon.Run to
avoid ambiguity or hiding global side effects inside packages.

closes #414

daemon/daemon.go

@@ -3,6 +3,7 @@ package daemon
 import (
 	"context"
 	"fmt"
+	"math/rand"
 	"os"
 	"os/signal"
 	"strings"
@@ -38,6 +39,12 @@ func Run(ctx context.Context, conf *config.Config) error {
 		cancel()
 	}()
 
+	// The math/rand package is used presently for generating trace IDs, we
+	// seed it with the current time and pid so that the IDs are mostly
+	// unique.
+	rand.Seed(time.Now().UnixNano())
+	rand.Seed(int64(os.Getpid()))
+
 	outlets, err := logging.OutletsFromConfig(*conf.Global.Logging)
 	if err != nil {
 		return errors.Wrap(err, "cannot build logging from config")