[CI] Add JUnit output

Author: picandocodigo

elasticsearch-api/Gemfile

@@ -19,4 +19,5 @@ end
 group :development do
   gem 'rspec'
   gem 'pry-nav'
+  gem 'rspec_junit_formatter'
 end

elasticsearch-api/spec/spec_helper.rb

@@ -44,6 +44,7 @@ def self.included(context)
   config.include(HelperModule)
   config.formatter = 'documentation'
   config.color = true
+  config.add_formatter('RspecJunitFormatter', 'tmp/elasticsearch-api-junit.xml')
 end
 
 if ENV['COVERAGE'] && ENV['CI'].nil? && !RUBY_1_8