Add test on syslog-ng service

test/integration/syslog_ng/controls/syslog_ng.rb

 describe file('/etc/syslog-ng/syslog-ng.conf') do
   it { should exist }
 end
+
+describe sysv_service('syslog-ng') do
+  it { should be_installed }
+  it { should be_enabled }
+  it { should be_running }
+end