Bound testing time for riak_object_dvv_statem

On my box, this test was timing before it reached the required 1k tests.
This change uses testing_time instead of a fixed number of iterations.
On my box, I find that I still get close to 1k iteratons in.
Merge pull request #898 from basho/bugfix/dvv-set-eqc-timeout

Bound testing time for riak_object_dvv_statem