Add tool to package up built modules.

With this change, you can package up modules while avoiding installing
them to the system.img or userdata.img.
- build/core/tasks/tools/package-modules.mk
  You can use this template to package up modules into a zip file and
  preserve the installed file paths.
- LOCAL_PICKUP_FILES, you can use this variable to package up extra
  files/directories.

Bug: 13585955
Change-Id: I103042b24ccf17cf5dc90c016d97ed1dd293e50b
diff --git a/core/clear_vars.mk b/core/clear_vars.mk
index 9d83de9..1902d57 100644
--- a/core/clear_vars.mk
+++ b/core/clear_vars.mk
@@ -13,6 +13,7 @@
 OVERRIDE_BUILT_MODULE_PATH:=
 LOCAL_INSTALLED_MODULE:=
 LOCAL_INSTALLED_MODULE_STEM:=
+LOCAL_PICKUP_FILES:=
 LOCAL_UNINSTALLABLE_MODULE:=
 LOCAL_INTERMEDIATE_TARGETS:=
 LOCAL_UNSTRIPPED_PATH:=