add conf_ha_dns_prefix and conf_ha_dns_suffix

Allow customization for HA_DNS_PREFIX and HA_DNS_SUFFIX.

This PR is a subpart of https://github.com/openshift/puppet-openshift_origin/pull/371.
I can close https://github.com/openshift/puppet-openshift_origin/pull/371 if https://github.com/openshift/puppet-openshift_origin/pull/312 is merged