Add test which ensures that the AAE source worker doesn't deadlock when
waiting for responses from the process which is computing the hashtree
differences.
Unfortunately, this test uses timeouts because as the code currently
stands, I can't figure out a way to make it any cleaner.
Ensure that AAE replication is tested using all possible failure cases
when dealing with the riak_kv_index_hashtrees and failed connections.
First, use intercepts on riak_kv_vnode and riak_kv_index_hashtree to
ensure that we simulate errors on a per node basis, starting with the
source cluster and moving to the sink. Simulate ownership transfers,
locked and incomplete hashtrees. Verify partitions generate the correct
error count, after using a bounded set of retries, and finally remove
all intercepts and verify that the fullsync completes and all keys have
been migrated between the two clusters.
