Make inner classes static where appropriate

There are several classes that have inner classes not declared with the
'static' modifier.  For these classes Findbugs reports:

  This class is an inner class, but does not use its embedded reference
  to the object which created it.  This reference makes the instances of
  the class larger, and may keep the reference to the creator object alive
  longer than necessary.  If possible, the class should be made static.

Add a 'static' modifier on these classes.

Change-Id: I0244bb1cd5662398f79c61d442df815e3811bf12

gerrit-lucene/src/main/java/com/google/gerrit/lucene/LuceneIndexModule.java

@@ -54,7 +54,7 @@ public class LuceneIndexModule extends LifecycleModule {
     }
   }
 
-  private class MultiVersionModule extends LifecycleModule {
+  private static class MultiVersionModule extends LifecycleModule {
     @Override
     public void configure() {
       factory(OnlineReindexer.Factory.class);