RFR: Make Host::user return Optional<String>

[Robin Westberg]

On Thu, 13 Feb 2020 15:34:32 GMT, Erik Helin <ehelin at openjdk.org> wrote:

> Hi all,
> 
> please review this refactoring that makes `Host::user` return an
> `Optional<String>` to support cases when a username does not map to a user.
> 
> Testing:
> - `make test` passes on Linux x64
> 
> Thanks,
> Erik

Looks good!

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Marked as reviewed by rwestberg (Reviewer).

PR: https://git.openjdk.java.net/skara/pull/435