RFR: 2411: Host::user should throw when failing

[Erik Joelsson]

The implementations of Host::user are all currently returning Optional::empty on any error return code. This means a that a bot checking for the existence of a user encounters an error with a host, e.g. JBS, it will think the user doesn't exist and take actions based on that assumption. This would be correct if the server response was 404, but in all other cases, it would be better if the WorkItem failed to be automatically retried later.

This patch changes the onError lambda for these methods so that it only handles the 404 case, and in all other cases lets the RestException be thrown. This matches the behavior of most other methods in these classes.

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Commit messages:
 - SKARA-2411

Changes: https://git.openjdk.org/skara/pull/1698/files
  Webrev: https://webrevs.openjdk.org/?repo=skara&pr=1698&range=00
  Issue: https://bugs.openjdk.org/browse/SKARA-2411
  Stats: 5 lines in 3 files changed: 0 ins; 0 del; 5 mod
  Patch: https://git.openjdk.org/skara/pull/1698.diff
  Fetch: git fetch https://git.openjdk.org/skara.git pull/1698/head:pull/1698

PR: https://git.openjdk.org/skara/pull/1698