Support disabling NoteDb reads for tests

In I0a9eb0ad we fixed a NoteDb-specific issue where loading the
default search results page caused ChangeNotes to get loaded, despite
not causing changes to load from ReviewDb.

Support this configuration in tests by adding a method to
NotesMigration that is called in AbstractChangeNotes#load(). In
production this method always returns false so the cost is negligible.

Change-Id: I22622cb3c834eeb1391d5b80247beafe36fffedf

gerrit-acceptance-framework/src/test/java/com/google/gerrit/acceptance/AbstractDaemonTest.java

@@ -529,6 +529,16 @@ public abstract class AbstractDaemonTest {
         atrScope.newContext(reviewDbProvider, null, anonymousUser.get()));
   }
 
+  protected Context disableDb() {
+    notesMigration.setFailOnLoad(true);
+    return atrScope.disableDb();
+  }
+
+  protected void enableDb(Context preDisableContext) {
+    notesMigration.setFailOnLoad(false);
+    atrScope.set(preDisableContext);
+  }
+
   protected static Gson newGson() {
     return OutputFormat.JSON_COMPACT.newGson();
   }