build script: fix error handler
build script:
Avoiding "perl: warning: Setting locale failed." as suggested on
https://wiki.ubuntu.com/DebootstrapChroot and
https://lists.debian.org/debian-amd64/2005/08/msg00249.html by setting
export LANG="C"
output
build script: chroot.d and postinst.d scripts: Explicitly "exit 0", so eventually trapped errors can be ignored.
improved error handler
build script: improved chroot scripts error handlers
build script: improved postinst.d scripts error handlers