v2.2.3: Merge pull request #42 from SimonRichardson/os-from-series-with-base-os
https://github.com/juju/os/pull/42 The following function helps provide a hint to help when normalising the OS from a series. For OSes like centos that just have a number after it, then the series of centos7 is fine, but fails when someone wants to just pass 7. Unless we know the potential os as a hint (centos) then we can then correctly normalise the value.