Add a default lsbmajdistrelease fact
Add a default lsbmajdistrelease fact

This is set to our current default choice of Ubuntu version. Having this fact fixes
issues in govuk_postgresql, puppet and puppetdb specs.

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