Bump Linux kernel to 'linux-image-4.4.0-231-generic'
Bump Linux kernel to 'linux-image-4.4.0-231-generic'

See https://ubuntu.com/security/notices/USN-5557-1

Trello: https://trello.com/c/ty5mtAL7/2960-look-into-linux-kernel-vulnerabilities

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