use rspec-puppet-facts for plugin_spec

spec/defines/plugin_spec.rb

@@ -1,18 +1,15 @@
 require 'spec_helper'
 
 describe 'fluentd::plugin' do
-  let(:facts) {
-    {
-      :osfamily        => 'Debian',
-      :lsbdistid       => 'Ubuntu',
-      :operatingsystem => 'Ubuntu',
-      :lsbdistcodename => 'precise',
-      :architecture    => 'amd64',
-    }
-  }
+  on_supported_os.each do |os, facts|
+    context "on #{os}" do
+      let :facts do
+        facts
+      end
+
       let(:pre_condition) { 'include fluentd' }
 
-  context 'gem plugin' do
+      describe 'gem plugin' do
         let(:title) { 'fluent-plugin-elasticsearch' }
         let(:params) do
           {
@@ -29,7 +26,7 @@ describe 'fluentd::plugin' do
         end
       end
 
-  context 'file plugin' do
+      describe 'file plugin' do
         let(:title) { 'fluent-plugin-test' }
         let(:params) do
           {
@@ -50,3 +47,5 @@ describe 'fluentd::plugin' do
         end
       end
     end
+  end
+end