Use crossystem rather than cros_boot_mode.

Also, make the check for normal mode a bit more restrictive.

BUG=chromium-os:13283
TEST=unit tests, tested on device

Change-Id: I3ec8a4c5526208d6f050ec2e152604b2ead76f27

Review URL: http://codereview.chromium.org/6719012
diff --git a/setup_dev_packages b/setup_dev_packages
index 8a9182c..64d063e 100755
--- a/setup_dev_packages
+++ b/setup_dev_packages
@@ -7,10 +7,10 @@
 set -ex
 
 sudo USE="-crash cros-debug" emerge -DNauv1 \
-  chromeos-base/cros_boot_mode \
   chromeos-base/hard-host-depends \
   chromeos-base/libchrome \
   chromeos-base/metrics \
+  chromeos-base/vboot_reference \
   dev-cpp/gmock \
   dev-cpp/gtest \
   dev-util/bsdiff \