bisect-kit: always run 'cros flash' inside chromeos chroot

'cros flash' may have extra dependencies (cherrypy for now) and thus
failed to run outside the chroot. In order to get rid of this kind of
problem, let's always run 'cros flash' inside chroot.

BUG=b:117050175
TEST=run bisect-kit on a clean linux machine

Change-Id: Ieee53f5034d4aaff20067acdfaafe322a07c494a
Reviewed-on: https://chromium-review.googlesource.com/1354840
Commit-Ready: Kuang-che Wu <kcwu@chromium.org>
Tested-by: Kuang-che Wu <kcwu@chromium.org>
Reviewed-by: Chung-yih Wang <cywang@chromium.org>
diff --git a/bisect_kit/cros_util.py b/bisect_kit/cros_util.py
index 59de98b..83b627c 100644
--- a/bisect_kit/cros_util.py
+++ b/bisect_kit/cros_util.py
@@ -392,8 +392,7 @@
                image_path,
                version=None,
                clobber_stateful=False,
-               disable_rootfs_verification=True,
-               run_inside_chroot=False):
+               disable_rootfs_verification=True):
   """Flash a DUT with given ChromeOS image.
 
   This is implemented by 'cros flash' command line.
@@ -409,7 +408,6 @@
     clobber_stateful: Clobber stateful partition when performing update
     disable_rootfs_verification: Disable rootfs verification after update
         is completed
-    run_inside_chroot: if True, run 'cros flash' command inside the chroot
   """
   logger.info('cros_flash %s %s %s %s', host, board, version, image_path)
 
@@ -423,10 +421,7 @@
   if disable_rootfs_verification:
     args.append('--disable-rootfs-verification')
 
-  if run_inside_chroot:
-    cros_sdk(chromeos_root, 'cros', 'flash', *args)
-  else:
-    util.check_call('chromite/bin/cros', 'flash', *args, cwd=chromeos_root)
+  cros_sdk(chromeos_root, 'cros', 'flash', *args)
 
   if version:
     # In the past, cros flash may fail with returncode=0