Rename rootsChanged to rootSetChan

No longer implies that the RootSetID changes between messages.

rootsanalyzer/rootsanalyzer.go

@@ -54,7 +54,7 @@ type incidentTemplateArgs struct {
 
 // Run starts a Roots Analyzer, which watches a CT log's root certificates and creates incident reports for changes to them.
 func Run(ctx context.Context, st storage.RootsReader, rep incident.Reporter, l *ctlog.Log) {
-	rootsChanged, err := st.WatchRoots(ctx, l)
+	rootSetChan, err := st.WatchRoots(ctx, l)
 	if err != nil {
 		glog.Errorf("%s: %s: storage.RootsReader.WatchRoots() = %q", l.URL, logStr, err)
 		return
@@ -65,7 +65,7 @@ func Run(ctx context.Context, st storage.RootsReader, rep incident.Reporter, l *
 		select {
 		case <-ctx.Done():
 			return
-		case rootSetID := <-rootsChanged:
+		case rootSetID := <-rootSetChan:
 			if lastRootSetID != "" && lastRootSetID != rootSetID {
 				// TODO(RJPercival): If the root set is flapping back to what it recently was, suppress sending an incident report
 				// since it could just be the result of skew between log frontends. However, if it doesn't flap back to the new