Use synchronous calls to update index hashtree

Port of basho/riak_kv@7596b4a920719e32ddff73385804aff943533fee

I choose to go with a 1s timeout because it still achieves the same
goal of applying back pressure but avoids blocking the vnode
indefinitely.

I also didn't match for Tree == 'undefined' because the calling code
never passed undefined.
Properly close hashtrees

Port of basho/riak_kv@835a79bbcb2dd219a4e7547353156a9f5b5078ff
Merge branch 'port-aae-updates-2'