Make all kind of timeouts hitting Riak configurable

This branch still has an easy bug, but sending it out to keep tracking. I'd be more than happy if somebody takes this (or it's also fine to omit and start a completely new work).
This very line causes [this](https://github.com/basho/riak_cs/blob/develop/riak_test/tests/cs743_regression_test.erl#L72) assertion in the `cs743_regression_test` to fail which is actually a good thing because it means the calculation is actually returning instead of timing out. I tried even up to 10000 objects and the test still passed. I will update to the test to expect success now instead of timeout.