Go to suspended before waiting for GC to complete.

We are not allowed to wait on the GC complete lock while holding the
mutator lock.

Bug: 38449715
Bug: 38350590

Test: test-art-host

(cherry picked from commit b93d5b1f)

Change-Id: Ib5b6d99b82f0c4a999bfcbbb1f5271da41a51040