Rework and rename verify_mw_timeouts test.

- test now called verify_api_timeouts
 - tests HTTP and PBC interfaces
 - now uses the RT clients
 - uses newly-added client features, reliant on:
   - riak-erlang-http-client commit 6733918
   - riak-erlang-client commit d2df4ef  which also depends on
   - riak_pb commit f73e1db