Delete a change from the index when it is not in the DB

If for some reason the secondary index is out of date, i.e. the  change
was deleted from the database but wasn't deleted from the secondary
index, it was impossible to re-index (remove) that change.

Add logic to automatically remove the change from the secondary index
if this change is requested through the Change REST API endpoint and
doesn't exist in the database.

If a user click on search result from a stale change, he will a get a
404 page and the change will be removed from the index.

To fix the problem without opening the change page, run a command like:
curl --user <user name>  -X POST http://<host>:<port>/a/changes/<change id>/index

Issue: 2996
Change-Id: I1db5373e31585e99c5f45e05274d86d69b4f24e6

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

@@ -322,6 +322,19 @@ public class LuceneChangeIndex implements ChangeIndex {
     }
   }
 
+  @SuppressWarnings("unchecked")
+  @Override
+  public void delete(int id) throws IOException {
+    Term idTerm = QueryBuilder.idTerm(id);
+    try {
+      Futures.allAsList(
+          openIndex.delete(idTerm),
+          closedIndex.delete(idTerm)).get();
+    } catch (ExecutionException | InterruptedException e) {
+      throw new IOException(e);
+    }
+  }
+
   @Override
   public void deleteAll() throws IOException {
     openIndex.deleteAll();

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

@@ -55,6 +55,10 @@ public class QueryBuilder {
     return intTerm(ID_FIELD, cd.getId().get());
   }
 
+  public static Term idTerm(int id) {
+    return intTerm(ID_FIELD, id);
+  }
+
   private final Schema<ChangeData> schema;
   private final org.apache.lucene.util.QueryBuilder queryBuilder;