ElasticV{6,7}QueryChangesTest: Add comment about issue 10120

Add a comment to clarify that the index close operation is done
to prevent issue 10120.

Change-Id: Id8d5b4e922674404351ac9a5a7a281283485fdb1
diff --git a/javatests/com/google/gerrit/elasticsearch/ElasticV6QueryChangesTest.java b/javatests/com/google/gerrit/elasticsearch/ElasticV6QueryChangesTest.java
index f1dcbaf..3f59d30 100644
--- a/javatests/com/google/gerrit/elasticsearch/ElasticV6QueryChangesTest.java
+++ b/javatests/com/google/gerrit/elasticsearch/ElasticV6QueryChangesTest.java
@@ -57,6 +57,8 @@
 
   @After
   public void closeIndex() {
+    // Close the index after each test to prevent exceeding Elasticsearch's
+    // shard limit (see Issue 10120).
     client.execute(
         new HttpPost(
             String.format(
diff --git a/javatests/com/google/gerrit/elasticsearch/ElasticV7QueryChangesTest.java b/javatests/com/google/gerrit/elasticsearch/ElasticV7QueryChangesTest.java
index 704f2f1..979a7f6 100644
--- a/javatests/com/google/gerrit/elasticsearch/ElasticV7QueryChangesTest.java
+++ b/javatests/com/google/gerrit/elasticsearch/ElasticV7QueryChangesTest.java
@@ -57,6 +57,8 @@
 
   @After
   public void closeIndex() {
+    // Close the index after each test to prevent exceeding Elasticsearch's
+    // shard limit (see Issue 10120).
     client.execute(
         new HttpPost(
             String.format(