Allow vendors to extend the list of public libs

The system is allowed to load libraries specified
in /vendor/etc/public.libraries.txt from /vendor/lib

Bug: http://b/27073931
Bug: http://b/26894351
Change-Id: I6b7bd077843810f5166e47095750bc8f33c344cf
(cherry picked from commit c554c8ae15b6ecbbf5ed1c98276aee591de7e765)
3 files changed