Notify Govuk::Gor when hosts change
Notify Govuk::Gor when hosts change

Prior to the changes in d2f9754c, Govuk::Gor was notified whenever the
`host` resouce changed.

Note that 'notify' implies 'before'; it ensures that the `host`
resources will be created before the `Govuk::Gor` class.

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