Replace public library list with shared lib sonames (part 2/2)

This commit updates interface of libdl.c.

1. android_init_namespaces is replaces with android_init_anonymous_namespace
2. added 2 arguments to android_create_namespace to specify linked namespace
   and the list of shared libraries sonames.
3. symbol lookup does not get past boundary libraries (added check and test for it).

Bug: http://b/26833548
Bug: http://b/21879602
Test: bionic-unit-tests --gtest_filter=dl*:Dl*
Change-Id: I32921da487a02e5bd0d2fc528904d1228394bfb9