RFR: 8300099: Configuration fails to auto-detect build user through $USER in dockers

[Aleksey Shipilev]

On Fri, 13 Jan 2023 04:10:16 GMT, Jie Fu <jiefu at openjdk.org> wrote:

> Hi all,
> 
> Configuration is broken in dockers after JDK-8296478.
> This is because `$USER` is not defined in dockers [1].
> 
> The fix will check `whoami` if we get an empty `$USERNAME`.
> 
> Thanks.
> Best regards,
> Jie
> 
> [1] https://stackoverflow.com/questions/54411218/docker-why-isnt-user-environment-variable-set

I am seeing a relevant failure on some of my Windows machines that run buildbot in "anonymous" shells. `whoami` exists there, so this PR should fix that trouble.

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PR: https://git.openjdk.org/jdk/pull/11983