ReviewerResource: Rename getUser to getReviewerUser

This avoids ambiguity with the user inherited from the ChangeResource.

Change-Id: If8e486fc42dab8d4439bf6465847fd34b99dca13

gerrit-server/src/main/java/com/google/gerrit/server/change/ReviewerJson.java

@@ -67,7 +67,7 @@ public class ReviewerJson {
     AccountLoader loader = accountLoaderFactory.create(true);
     for (ReviewerResource rsrc : rsrcs) {
       ReviewerInfo info = format(new ReviewerInfo(
-          rsrc.getUser().getAccountId()),
+          rsrc.getReviewerUser().getAccountId()),
           rsrc.getUserControl());
       loader.put(info);
       infos.add(info);