Update code and tests to match aws_sigv4 faraday middleware

Signed-off-by: Balasankar "Balu" C <balasankarc@autistici.org>

ee/lib/gitlab/elastic/client.rb

 # frozen_string_literal: true
 
+require 'faraday_middleware/aws_sigv4'
+
 module Gitlab
   module Elastic
     module Client
@@ -17,7 +19,7 @@ module Gitlab
           region = config[:aws_region]
 
           ::Elasticsearch::Client.new(base_config) do |fmid|
-            fmid.request(:aws_signers_v4, credentials: creds, service_name: 'es', region: region)
+            fmid.request(:aws_sigv4, credentials: creds, service: 'es', region: region)
           end
         else
           ::Elasticsearch::Client.new(base_config)

ee/spec/lib/gitlab/elastic/client_spec.rb

@@ -28,6 +28,8 @@ describe Gitlab::Elastic::Client do
       .to_return(status: 200, body: "RoleName", headers: {})
     stub_request(:get, "http://169.254.169.254/latest/meta-data/iam/security-credentials/RoleName")
       .to_return(status: 200, body: creds_response, headers: {})
+    stub_request(:put, "http://169.254.169.254/latest/api/token")
+      .to_return(status: 200, body: "", headers: {})
   end
 
   describe '.build' do
@@ -62,8 +64,13 @@ describe Gitlab::Elastic::Client do
           stub_request(:get, 'http://example-elastic:9200/foo/_all/1')
             .with(
               headers: {
-                'Authorization'        => 'AWS4-HMAC-SHA256 Credential=0/20170303/us-east-1/es/aws4_request, SignedHeaders=content-type;host;x-amz-content-sha256;x-amz-date, Signature=4ba2aae19a476152dacf5a2191da67b0cf81b9d7152dab5c42b1bba701da19f1',
+                'Accept'               => '*/*',
+                'Accept-Encoding'      => 'gzip,deflate',
+                'Authorization'        => 'AWS4-HMAC-SHA256 Credential=0/20170303/us-east-1/es/aws4_request, SignedHeaders=content-type;host;user-agent;x-amz-content-sha256;x-amz-date, Signature=e52132ac542972698e99d9a8337b7493e4ca6210f61fc8da5cbb8008d8b2fb87',
                 'Content-Type'         => 'application/json',
+                'Date'                 => 'Fri, 03 Mar 2017 13:39:52 GMT',
+                'Host'                 => 'example-elastic:9200',
+                'User-Agent'           => 'Faraday v0.15.4',
                 'X-Amz-Content-Sha256' => 'e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855',
                 'X-Amz-Date'           => '20170303T133952Z'
               })