Index.replace: Log responses containing errors

Logging errors can help with triage.

Change-Id: Idefb8dacd0b3fb51f1006f947873dc92ffbd641f
diff --git a/src/main/java/com/google/gerrit/elasticsearch/AbstractElasticIndex.java b/src/main/java/com/google/gerrit/elasticsearch/AbstractElasticIndex.java
index 1aac6e7..482868c 100644
--- a/src/main/java/com/google/gerrit/elasticsearch/AbstractElasticIndex.java
+++ b/src/main/java/com/google/gerrit/elasticsearch/AbstractElasticIndex.java
@@ -284,7 +284,11 @@
           String.format("Expected %s, but was: %s", ContentType.APPLICATION_JSON, contentType));
       String responseStr = EntityUtils.toString(response.getEntity());
       JsonObject responseJson = (JsonObject) new JsonParser().parse(responseStr);
-      return responseJson.get("errors").getAsBoolean();
+      boolean hasErrors = responseJson.get("errors").getAsBoolean();
+      if (hasErrors) {
+        logger.atSevere().log("Response with errors: %s", responseJson);
+      }
+      return hasErrors;
     } catch (IOException e) {
       throw new StorageException(e);
     }