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.
Merge pull request #788 from basho/jrw-fix-put-fsm-preflist-choice

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