rootdir: Create folders in Android.mk

system.img may contain the root directory as well. In that case, we
need to create some folders init.rc would during the build.

Change-Id: I157ccbebf36bee9916f3f584551704ec481ae1d1
diff --git a/rootdir/Android.mk b/rootdir/Android.mk
index 7ab76b8..c652f7c 100644
--- a/rootdir/Android.mk
+++ b/rootdir/Android.mk
@@ -26,7 +26,7 @@
 #
 # create some directories (some are mount points)
 LOCAL_POST_INSTALL_CMD := mkdir -p $(addprefix $(TARGET_ROOT_OUT)/, \
-    sbin dev proc sys system data oem)
+    sbin dev proc sys system data oem acct config storage mnt root)
 
 include $(BUILD_SYSTEM)/base_rules.mk