Move ipv6only=on option from template into puppet
See jfryman#30
Update tests accroding to changed templates

Specs no longer require `ipv6only=on` in listen option when using user
supplied value since it is no longer hardcoded in the template.
Merge pull request #249 from fadenb/bug/duplicate_listen_option_ipv6only

Bugfix for duplicate listen option caused by hardcoded `ipv6only=on` in template