Add ability to blacklist packages from chromeos-base/chromeos.

get_package_list

Index: get_package_list
diff --git a/get_package_list b/get_package_list
index 0deb1f0a6a7e92b3b6edd1fd7e55cb19d3da7939..b45e2869ada3f9ce216009ec301b62154b1139ec 100755
--- a/get_package_list
+++ b/get_package_list
@@ -20,11 +20,13 @@ DEFINE_string board "$DEFAULT_BOARD" \
 
 # Parse flags.
 FLAGS "$@" || exit 1
+eval set -- "${FLAGS_ARGV}"
+
+[[ -z "${FLAGS_board}" ]] && die "A board must be specified."
 
 if [[ -z "${FLAGS_ARGV}" ]]; then
-  echo "Please specify package."
-  echo "Usage:  ./get_package_list.sh chromeos-base/chromeos > package.list"
-  exit 1
+  warn "Please specify package."
+  die "Usage:  ./get_package_list.sh chromeos-base/chromeos > package.list"
 fi
 
 emerge-$FLAGS_board --emptytree --usepkgonly -p -v --columns \