dev_install: Exclude the var symlink when packaging dev-only files.

When running dev_install, the directory /usr/local/var already exists
so extracting dev-only-extras.tbz2 on /usr/local fails since it
contains "var" as a symlink.

The contents installed in /usr/local/var are already present in the
stateful partition since we created a symlink from there.

BUG=chromium:381886
TEST=`./build_image` creates the .tbz2 file without var symlink.

Change-Id: I5b299398d0b09ef6babd6164b3ae5d47282ad13e
Reviewed-on: https://chromium-review.googlesource.com/245480
Tested-by: Alex Deymo <deymo@chromium.org>
Reviewed-by: Mike Frysinger <vapier@chromium.org>
Commit-Queue: Alex Deymo <deymo@chromium.org>
Trybot-Ready: Alex Deymo <deymo@chromium.org>
diff --git a/build_library/base_image_util.sh b/build_library/base_image_util.sh
index 2efac30..34c37b0 100755
--- a/build_library/base_image_util.sh
+++ b/build_library/base_image_util.sh
@@ -222,10 +222,14 @@
   # Create a package for the dev-only files installed in /usr/local of a base
   # image. This package can later be downloaded with dev_install running from
   # a base image.
+  # Files installed in /usr/local/var were already installed in stateful since
+  # we created a symlink for those. We ignore the symlink in this package since
+  # the directory /usr/local/var exists in the target image when dev_install
+  # runs.
   # TODO(deymo): Move dev-only-extras.tbz2 outside packages. See
   # crbug.com/448178 for details.
   sudo tar -cf "${BOARD_ROOT}/packages/dev-only-extras.tbz2" -I pbzip2 \
-    -C "${root_fs_dir}/usr/local" .
+    --exclude=var -C "${root_fs_dir}/usr/local" .
 
   # Zero rootfs free space to make it more compressible so auto-update
   # payloads become smaller