Make ELASTICSEARCH_URI point to ES6
Make ELASTICSEARCH_URI point to ES6

This makes the A and B cluster environment variables refer to the same
place, but search-api has been deployed with the A cluster disabled,
so this is safe to do.

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