Elasticsearch: replace native API in prod w/ REST

Remove jest API which depends on Elasticsearch native API (also
removed), so no longer depend on lucene for this scope. Replace such
removed dependencies with the Elasticsearch low-level API, which does
not depend on Lucene. That now used API is a REST client with minimal
dependencies, indeed. -As opposed to Elastic's current high-level API,
which still depends on lucene and other Gerrit-constraining libraries.

Do so in order to decouple the elasticsearch client from lucene in
Gerrit. That REST client does not logically require Lucene anyway. Most
importantly, such decoupling now enables upcoming support for more than
just one Elasticsearch server version. This includes the new possibility
of bumping the latter to multiple yet later versions, such as 5 and 6.x.
The currently used version (2.4) should also still be kept, for a while.

Bumping such versions will likely require some Elasticsearch client code
adaptations, so that Gerrit can (dynamically?) switch between either
Elasticsearch server version to eventually support (hopefully soon).

Doing the same for the elasticsearch tests in Gerrit is to be done using
another change or more changes.

Add a partial and customized fork of [1], based on [1]'s commit [2], to
preserve the ability of building proper json requests for Elasticsearch.
Put that forked json-generating code under a new 'builders' sub-package.
There should be a possibility in some near future to consider removing
that fork, based on potential progress such as the one proposed in [3].
Meanwhile, this fork shall be maintained to usual Gerrit quality levels.

[1] https://github.com/elastic/elasticsearch
[2] tag: v2.4.4
[3] https://github.com/elastic/elasticsearch/issues/30791

Bug: Issue 6094
Change-Id: I720c9885c9eab2388acc328eecb9eaa6940ced0c

java/com/google/gerrit/elasticsearch/ElasticConfiguration.java

@@ -18,13 +18,12 @@ import com.google.common.base.MoreObjects;
 import com.google.gerrit.server.config.GerritServerConfig;
 import com.google.inject.Inject;
 import com.google.inject.Singleton;
-import java.net.MalformedURLException;
-import java.net.URL;
 import java.util.ArrayList;
-import java.util.Arrays;
+import java.util.Collections;
 import java.util.List;
 import java.util.Set;
 import java.util.concurrent.TimeUnit;
+import org.apache.http.HttpHost;
 import org.eclipse.jgit.lib.Config;
 
 @Singleton
@@ -33,7 +32,7 @@ class ElasticConfiguration {
   private static final String DEFAULT_PORT = "9200";
   private static final String DEFAULT_PROTOCOL = "http";
 
-  final List<String> urls;
+  final List<HttpHost> urls;
   final String username;
   final String password;
   final boolean requestCompression;
@@ -59,14 +58,18 @@ class ElasticConfiguration {
 
     Set<String> subsections = cfg.getSubsections("elasticsearch");
     if (subsections.isEmpty()) {
-      this.urls = Arrays.asList(buildUrl(DEFAULT_PROTOCOL, DEFAULT_HOST, DEFAULT_PORT));
+      HttpHost httpHost =
+          new HttpHost(DEFAULT_HOST, Integer.valueOf(DEFAULT_PORT), DEFAULT_PROTOCOL);
+      this.urls = Collections.singletonList(httpHost);
     } else {
       this.urls = new ArrayList<>(subsections.size());
       for (String subsection : subsections) {
         String port = getString(cfg, subsection, "port", DEFAULT_PORT);
         String host = getString(cfg, subsection, "hostname", DEFAULT_HOST);
         String protocol = getString(cfg, subsection, "protocol", DEFAULT_PROTOCOL);
-        this.urls.add(buildUrl(protocol, host, port));
+
+        HttpHost httpHost = new HttpHost(host, Integer.valueOf(port), protocol);
+        this.urls.add(httpHost);
       }
     }
   }
@@ -74,19 +77,4 @@ class ElasticConfiguration {
   private String getString(Config cfg, String subsection, String name, String defaultValue) {
     return MoreObjects.firstNonNull(cfg.getString("elasticsearch", subsection, name), defaultValue);
   }
-
-  private String buildUrl(String protocol, String hostname, String port) {
-    try {
-      return new URL(protocol, hostname, Integer.parseInt(port), "").toString();
-    } catch (MalformedURLException | NumberFormatException e) {
-      throw new RuntimeException(
-          "Cannot build url to Elasticsearch from values: protocol="
-              + protocol
-              + " hostname="
-              + hostname
-              + " port="
-              + port,
-          e);
-    }
-  }
 }