Add rootdev to AU's dev packages.

BUG=5938
TEST=ran ./setup_dev_packages and CFLAGS=-O1 ./gen_coverage_html.sh

Change-Id: I0c47254c96d06e31345c42bd41f157588292b587

Review URL: http://codereview.chromium.org/3238013
diff --git a/setup_dev_packages b/setup_dev_packages
index a8e6a7e..5c4accb 100755
--- a/setup_dev_packages
+++ b/setup_dev_packages
@@ -13,4 +13,5 @@
   dev-cpp/gtest \
   dev-util/bsdiff \
   dev-util/lcov \
-  sys-apps/fakeroot
+  sys-apps/fakeroot \
+  sys-apps/rootdev