Update repair count type specs in riak_kv_entropy_info

Change the repaired field of the exchange_info record in the
riak_kv_entropy_info module from a type of pos_integer() to
non_neg_integer(). Also change the Repaired parameter type for
riak_kv_entropy_info:exchange_complete/4 and
riak_kv_entropy_info:exchange_complete/5 to be non_neg_integer().
Merge pull request #947 from basho/bugfix/kv-entropy-info-specs

Update repair count type specs in riak_kv_entropy_info

Reviewed-by: reiddraper