Sort collector names in startup logs (#857)

Signed-off-by: Brian Brazil <brian.brazil@robustperception.io>

node_exporter.go

@@ -17,6 +17,7 @@ import (
 	"fmt"
 	"net/http"
 	_ "net/http/pprof"
+	"sort"
 
 	"github.com/prometheus/client_golang/prometheus"
 	"github.com/prometheus/client_golang/prometheus/promhttp"
@@ -87,7 +88,12 @@ func main() {
 		log.Fatalf("Couldn't create collector: %s", err)
 	}
 	log.Infof("Enabled collectors:")
+	collectors := []string{}
 	for n := range nc.Collectors {
+		collectors = append(collectors, n)
+	}
+	sort.Strings(collectors)
+	for _, n := range collectors {
 		log.Infof(" - %s", n)
 	}