Only bind index {start/activate} if needed

These commands are only interacting with the AbstractVersionManager, if
it is not available then they have no reason to be available.

Because those commands were always binded, binding an implementation of
AbstractVersionManager was mandatory otherwise Guice would have
complained. For that reason, the implementation of
AbstractVersionManager was done even in the case when index is a single
version and an implementation of AbstractVersionManager is not required.
Only bind implementations of AbstractVersionManager when needed and bind
the commands only if AbstractVersionManager implementation is binded.

Change-Id: I3db48f6b5d030ecc6efa840c59eb4e177ae1b6b1

gerrit-elasticsearch/src/main/java/com/google/gerrit/elasticsearch/ElasticIndexModule.java

@@ -64,11 +64,11 @@ public class ElasticIndexModule extends LifecycleModule {
 
     install(new IndexModule(threads));
     if (singleVersions == null) {
+      bind(AbstractVersionManager.class).to(ElasticVersionManager.class);
       listener().to(ElasticVersionManager.class);
     } else {
       install(new SingleVersionModule(singleVersions));
     }
-    bind(AbstractVersionManager.class).to(ElasticVersionManager.class);
   }
 
   @Provides