RFR: Add HostUserDetails::email

[Erik Helin]

Hi all,

please review this patch that adds the method `HostUserDetails::email`. It is
rare for user to have public emails, but the bots can now take advantage of
those rare cases.

Testing:
- `make test` on Linux x64 passes

Thanks,
Erik

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Commits:
 - c77e1d95: Add HostUserDetails::email

Changes: https://git.openjdk.java.net/skara/pull/436/files
 Webrev: https://webrevs.openjdk.java.net/skara/436/webrev.00
  Stats: 28 lines in 3 files changed: 25 ins; 0 del; 3 mod
  Patch: https://git.openjdk.java.net/skara/pull/436.diff
  Fetch: git fetch https://git.openjdk.java.net/skara pull/436/head:pull/436

PR: https://git.openjdk.java.net/skara/pull/436