Wrap get_distribution_version() in the hostname module

We wrap get_distribution_version() with a new function,
_get_distribution_version(), that returns `0` when the result is a string or
`None`.

This accounts for the case when get_distribution_version() returns a string,
and we try to compare it to a float. We do this in the hostname module instead
of the module snippets because other modules may want the real string
version.module snippets because other modules may want the real string version.
Merge pull request #8311 from neersighted/wrap_distroversion

Wrap get_distribution_version() in the hostname module