Refactor state tracking (...)

Move state tracking into the puller/scanner objects. This is a first
step towards resolving #1391.

Rename Puller and Scanner to roFolder and rwFolder as they have more
duties than just pulling and scanning, and don't need to be exported.

test/ignore_test.go

@@ -13,6 +13,7 @@ import (
 	"os"
 	"path/filepath"
 	"testing"
+	"time"
 
 	"github.com/syncthing/syncthing/internal/symlinks"
 )
@@ -71,7 +72,22 @@ func TestIgnores(t *testing.T) {
 
 	// Rescan and verify that we see them all
 
-	p.post("/rest/scan?folder=default", nil)
+	// Wait for one scan to succeed, or up to 20 seconds...
+	// This is to let startup, UPnP etc complete.
+	for i := 0; i < 20; i++ {
+		resp, err := p.post("/rest/scan?folder=default", nil)
+		if err != nil {
+			time.Sleep(time.Second)
+			continue
+		}
+		if resp.StatusCode != 200 {
+			resp.Body.Close()
+			time.Sleep(time.Second)
+			continue
+		}
+		break
+	}
+
 	m, err := p.model("default")
 	if err != nil {
 		t.Fatal(err)