fix put fsm's use of random:uniform_s when choosing forwarding node

* uniform_s/2 returns a 2-tuple instead of just the randomly generated integer
* uniform_s/2 replaced crypto:rand_uniform/2. However, while the former is inclusive
of the upper bound the latter is not.

http://www.erlang.org/doc/man/random.html#uniform_s-2
http://www.erlang.org/doc/man/crypto.html#rand_uniform-2

Failure found via `http_bucket_types`, reproduced locally. I've verified this fixes the test for me....

http://giddyup.basho.com/#/projects/riak_ee/scorecards/66/66-1537-http_bucket_types-centos-6-64-eleveldb/30414/artifacts/423757