Adding ensure parameter to varnish::logging

This will allow us to ensure that a varnishncsa service
is stopped via puppet.  I plan to use this to disable
the emery varnishncsa instance and start up a new one
for erbium.

See RT 6143

Change-Id: If4ccd314a3b8d42b4c74fbcf2e0129dfa07eabc4