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/ReviewerResource.java

@@ -47,7 +47,7 @@ public class ReviewerResource extends ChangeResource {
     this(rsrc, userFactory.create(id));
   }
 
-  public IdentifiedUser getUser() {
+  public IdentifiedUser getReviewerUser() {
     return user;
   }