build.sh: Show all timestamps in UTC (v3.3.28)

:Release Notes:
The time format ends with "Z" as "Zulu" so use -u as "UTC".

:Detailed Notes:

:Testing Performed:
Only build tested.

:QA Notes:
No change to image.

:Issues Addressed:
[ES-1095] human-readable timestamps in build logs imply "Zulu" time but
          are actually local

Open-webOS-DCO-1.0-Signed-off-by: Martin Jansa <martin.jansa@lge.com>
Change-Id: I93774e23ab7204e0459c87c014304747312dca81
Reviewed-on: https://g2g.palm.com/6305
Reviewed-by: DCO Verification
Reviewed-by: Martin Jansa <Martin.Jansa@lge.com>
Tested-by: Martin Jansa <Martin.Jansa@lge.com>
Reviewed-by: Susan Montooth <susan.montooth@lge.com>