(PF-537) Fix nginx module isdefaultvhost declaration in erb and defined
types.

This change makes the server declaration a bit more configurable, it
allows you to turn on/off ipv6only=on  on the listen line independent of
isdefaultserver.

ref: https://chrisjean.com/2014/02/10/fix-nginx-emerg-bind-to-80-failed-98-address-already-in-use/

Also this commit:
- Adds fix to vhost erb
- Adds ipv6only flag to defined type.