Amazon Linux v2 detection is broken (os.version is 2.0, not 2017.12)

Previous to the release of Amazon Linux v2, facter reported the version of Amazon Linux as a date-based string, e.g "2017.09". In Amazon Linux v2, this has changed to "2.0".

The code changes previously made in Puppet's service provider code and acceptance tests have incorrectly assumed that Amazon Linux v2 returns a version of "2017.12" and will need to be updated to work with "2.0" instead.