Fix greylist exception to account for linked namespaces

Do not load second copy of libraries that are supposed to
be provided by linked namespaces. Also do not print
error in the log if caller tries to open shared library
using absolute path for apps targeting N+.

Bug: http://b/35454141
Bug: http://b/26833548
Bug: http://b/35338922
Test: run bionic-unit-tests --gtest_filter=dl*
Change-Id: Icf3aeedff18d287d2ba0b3df3808b100f3ef5f7a