fix is in cq right now, but it's been verified with trybot

https://chromium-review.googlesource.com/c/chromiumos/chromite/+/1058073

The following revision refers to this bug:
  https://chromium.googlesource.com/chromiumos/chromite/+/4c1562dfdeef52d791af660b49b620daea277738

commit 4c1562dfdeef52d791af660b49b620daea277738
Author: C Shapiro <shapiroc@chromium.org>
Date: Wed May 16 19:41:43 2018

cbuildbot: Fix file check outside chroot

The file check was happening outsite of the chroot, which never passed.
This worked until the dtb file was fully removed.

BUG= chromium:842834 
TEST=cros tryjob -g 1058073 nami-release-tryjob

Change-Id: I93bf5eee3cbae5906cd0b92d1164f3be84aaf2a9
Reviewed-on: https://chromium-review.googlesource.com/1058073
Commit-Ready: C Shapiro <shapiroc@google.com>
Tested-by: C Shapiro <shapiroc@google.com>
Reviewed-by: Lann Martin <lannm@chromium.org>

[modify] https://crrev.com/4c1562dfdeef52d791af660b49b620daea277738/cbuildbot/commands.py

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/4f522e01e2856828612aec72e303d3b870a78515

commit 4f522e01e2856828612aec72e303d3b870a78515
Author: chromite-chromium-autoroll@skia-buildbots.google.com.iam.gserviceaccount.com <chromite-chromium-autoroll@skia-buildbots.google.com.iam.gserviceaccount.com>
Date: Wed May 16 22:42:12 2018

Roll src/third_party/chromite/ 5f638a109..4c1562dfd (3 commits)

https://chromium.googlesource.com/chromiumos/chromite.git/+log/5f638a1091fb..4c1562dfdeef

$ git log 5f638a109..4c1562dfd --date=short --no-merges --format='%ad %ae %s'
2018-05-14 shapiroc cbuildbot: Fix file check outside chroot
2018-05-04 bmgordon cros_test_lib: Refactor cros_build_lib mocks
2018-05-12 yunlian cros_setup_toolchain: build toolchains in reversed order.

Created with:
  roll-dep src/third_party/chromite
BUG= chromium:842834 , chromium:809634 ,chromium:711369


The AutoRoll server is located here: https://chromite-chromium-roll.skia.org

Documentation for the AutoRoller is here:
https://skia.googlesource.com/buildbot/+/master/autoroll/README.md

If the roll is causing failures, please contact the current sheriff, who should
be CC'd on the roll, and stop the roller if necessary.


TBR=chrome-os-gardeners@chromium.org

Change-Id: Icd8ebd153995e7b541c78dc08f8072239c16a140
Reviewed-on: https://chromium-review.googlesource.com/1062649
Reviewed-by: Chromite Chromium Autoroll <chromite-chromium-autoroll@skia-buildbots.google.com.iam.gserviceaccount.com>
Commit-Queue: Chromite Chromium Autoroll <chromite-chromium-autoroll@skia-buildbots.google.com.iam.gserviceaccount.com>
Cr-Commit-Position: refs/heads/master@{#559319}
[modify] https://crrev.com/4f522e01e2856828612aec72e303d3b870a78515/DEPS