Add tree rebuild in 2i AAE test

This helps verify the problem where 2i AAE trees got dropped during a
rebuild, breaking future runs of the repair-2i command.
Enhanced the wait for AAE trees function to try a lock on the built
trees. The building process may have notified its end, but it is still
possible to get a not_built if you try to get a lock very quickly. This
attempts the lock for each partition before declaring total victory.

This verifies https://github.com/basho/riak_kv/pull/780

/cc @jtuple There is no pressure to immediately release a patch now, so when you are rested later, I would love your feedback on the test. It was kind of a pain to write and is not sleep free.  I think we can try to get some AAE changes for testability to improve on this.