Update default checkout location for checkout_aosp.py

Change-Id: Ic5b1f79628e90401b2cee1d3f705468c88e8b951
diff --git a/tools/utils_aosp.py b/tools/utils_aosp.py
index 8f20c2f..3e2a715 100644
--- a/tools/utils_aosp.py
+++ b/tools/utils_aosp.py
@@ -17,11 +17,14 @@
 
 DEFAULT_ROOT = join(utils.REPO_ROOT, 'build', 'aosp')
 
-def add_common_arguments(parser):
+def add_root_argument(parser):
   parser.add_argument('--aosp-root',
       help='Root of the AOSP checkout. ' +
            'Defaults to ' +  DEFAULT_ROOT +'.',
       default=DEFAULT_ROOT)
+
+def add_common_arguments(parser):
+  add_root_argument(parser)
   parser.add_argument('--lunch',
       help='Build menu. ' +
            'Defaults to ' + DEFAULT_LUNCH + '.',