/usr/share/live/images/gnome-desktop/auto/build is in open-infrastructure-system-images 20161101-lts2-2.
This file is owned by root:root, with mode 0o755.
The actual contents of the file can be viewed below.
1 2 3 4 5 | #!/bin/sh
set -e
lb build noauto "${@}" 2>&1 | tee build.log
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