Update Perl modules when making chroot.

This CL moves the Perl rebuild logic from update_chroot into a separate
script under build_library/perl_rebuild.sh, such that we can reuse the
code to update Perl modules in the early phase of make_chroot.

BUG=chromium:722063
TEST=Remote trybot run on chromiumos-sdk builder.

Change-Id: Ic0cbbbd8f98abca2c8e11e1adbae9aa2c0ea8a9c
Reviewed-on: https://chromium-review.googlesource.com/506432
Commit-Ready: Ben Chan <benchan@chromium.org>
Tested-by: Ben Chan <benchan@chromium.org>
Reviewed-by: Ben Chan <benchan@chromium.org>
3 files changed