RFR: 8277762: Allow configuration of HOTSPOT_BUILD_USER [v2]

[Andrew Leonard]

> To better allow "reproducible builds", a new configure parameter is added to set the USERNAME build variable, rather than always using the current user:
>     --with-build-user=<username> 
> HOTSPOT_BUILD_USER is then set to a reproducible USERNAME if required.
> 
> Signed-off-by: Andrew Leonard <anleonar at redhat.com>

Andrew Leonard has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains five additional commits since the last revision:

 - 8277762: Allow configuration of HOTSPOT_BUILD_USER
   
   Signed-off-by: Andrew Leonard <anleonar at redhat.com>
 - Merge branch 'master' of https://github.com/openjdk/jdk into builduser
 - 8277762: Allow configuration of HOTSPOT_BUILD_USER
   
   Signed-off-by: Andrew Leonard <anleonar at redhat.com>
 - 8277762: Allow configuration of HOTSPOT_BUILD_USER
   
   Signed-off-by: Andrew Leonard <anleonar at redhat.com>
 - 8277762: Allow configuration of HOTSPOT_BUILD_USER
   
   Signed-off-by: Andrew Leonard <anleonar at redhat.com>

-------------

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/6542/files
  - new: https://git.openjdk.java.net/jdk/pull/6542/files/f9fb274a..3896df55

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=6542&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=6542&range=00-01

  Stats: 6325 lines in 236 files changed: 4145 ins; 1326 del; 854 mod
  Patch: https://git.openjdk.java.net/jdk/pull/6542.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/6542/head:pull/6542

PR: https://git.openjdk.java.net/jdk/pull/6542