Add retry to ensure service is reachable

Also modify Gemfile for ruby version issue

test/integration/standard/serverspec/Gemfile

@@ -0,0 +1,3 @@
+source 'https://rubygems.org'
+
+gem 'rspec-retry'

test/integration/standard/serverspec/default_spec.rb

@@ -18,9 +18,14 @@ context "basic tests" do
     it { should be_file }
   end
 
-  describe command('curl localhost:9200/_nodes/?plugin | grep kopf') do
-    its(:stdout) { should match /kopf/ }
-    its(:exit_status) { should eq 0 }
+  describe 'plugin' do
+
+    it 'should be reported as existing', :retry => 3, :retry_wait => 10 do
+      command = command('curl localhost:9200/_nodes/?plugin | grep kopf')
+      expect(command.stdout).to match(/kopf/)
+      expect(command.exit_status).to eq(0)
+    end
+
   end
 
 end

test/integration/standard/serverspec/spec_helper.rb

@@ -1,2 +1,11 @@
 require 'serverspec'
 set :backend, :exec
+
+require 'rspec/retry'
+
+RSpec.configure do |config|
+  # show retry status in spec process
+  config.verbose_retry = true
+  # show exception that triggers a retry if verbose_retry is set to true
+  config.display_try_failure_messages = true
+end