Fix Rummager search index tests
Fix Rummager search index tests

In AWS the "Search Index" job failed because it was trying to connect to
localhost:9200. In Carrenza this is not an issue as there is a proxy
that listens on localhost, but in AWS we go directly to an Elastic Load
Balancer, and so requests to localhost would fail.

This was because the rake task that ran this particular test[1][] used the
ELASTICSEARCH_HOSTS environment variable to set the destination, rather
than ELASTICSEARCH_URI. These values should be exactly the same, so add
the additional environment variable.

This should be fixed in Rummager itself, but to ensure that nothing else
breaks when using this env var, ensure that it is set everywhere.

[1]https://github.com/alphagov/rummager/blob/master/lib/services.rb#L27

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