ART: Slightly change InitializeClass flow

Since 884f3b83, verification isn't
run completely under a class' lock. This means it is possible to
race from unverified to initialized in InitializeClass. So check
the class state after VerifyClass, and handle new success and
failure cases.

Bug: 28254258
Change-Id: I22a6121477e409987281bc81c28b6c942f1bd319