Changes to support remote exec for build_packages and enter_chroot.

enter_chroot:
add reclient_dir and reproxy_cfg_file flags in enter_chroot
so the location of those files can be mounted to chroot.

build_packages:
add a run_remoteexec flag.
If true, runs the reproxy binary with env RECLIENT_DIR and REPROXY_CFG
which will be passed in to chroot's env like this:
https://chromium-review.googlesource.com/c/chromiumos/chromite/+/3259256/6/cbuildbot/remoteexec_util.py

DEFINE_string reproxy_cfg_file

Change-Id: I0f369062e98c742382d712a33824977c1d4b4fcc
Bug: 1256966
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/crosutils/+/3277234
Reviewed-by: Alex Klein <saklein@chromium.org>
Tested-by: Joanna Wang <jojwang@chromium.org>
Commit-Queue: Joanna Wang <jojwang@chromium.org>
2 files changed