ART: Fix VISIT_OBJECTS and ABORT for FollowReferences

If a root report does not set VISIT_OBJECTS, the referree should
not be added to the worklist.

Whenever an ABORT is requested, do not report the remaining roots.

Bug: 36727422
Test: art/test.py --host -t 913
Change-Id: I942559f6ab356fe2573a3a9bb88b2662cd5b23d0