Use the full version string for grafana
Use the full version string for grafana

The apt command can't find a version called "3.1.1", even though the
cache contains all the versions we expect.

I'm assuming we need to add the postfix to the version numbers.

This is the output of `apt-cache policy grafana` on integration:

    grafana:
      Installed: 4.1.2-1486989747
      Candidate: 4.1.2-1486989747
      Version table:
     *** 4.1.2-1486989747 0
            500 http://apt.production.alphagov.co.uk/grafana/ jessie/main
    amd64 Packages
            100 /var/lib/dpkg/status
    [...]
         3.1.1-1470047149 0
            500 http://apt.production.alphagov.co.uk/grafana/ jessie/main
    amd64 Packages
    [...]

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