Fail hard if provided IP addresses are not valid
Fail hard if provided IP addresses are not valid

Rather than making the creation of DNS entries conditional on validity
of the IP addresses supplied, fail hard if the provided IP addresses are
not valid.

We always want these IPs to be valid and set, so we should fail quickly
if they are not.

alphagov/govuk-puppet,alphagov/govuk-puppet,alphagov/govuk-puppet,alphagov/govuk-puppet,alphagov/govuk-puppet,alphagov/govuk-puppet