Improved location claim algorithm

This PR adds a new v4 claim algorithm, which significantly improves the efficiency of claim with location awareness. The algorithm has a brute force approach, whereby it will in the plan stage potentially do an exhaustive search of the possible swaps and moves, in order to provide a ring which meets the target n_val for both nodes and locations. Firstly by trying to minimise the number of changes, and if that is unsuccessful it will attempt to find a valid solution without concern for the plan complexity. To enable the feature, set via riak.conf: `choose_claim_fun` -> `choose_claim_v4` `full_rebalance_onleave` -> `on` `target_n_val` -> `4` (default) `target_location_n_val -> `3` (default) riak_test testa are added and updated in https://github.com/basho/riak_test/pull/1375. There is a write-up in docs/claim-version4.md. In some cases cluster plans may take much longer than at present, potentially > 60s. The new claim algorithm was developed by [Ulf Norell and Thomas Arts](http://www.quviq.com/contact-2/about/).