Update riak/tests/test_all.py

* Explicitly set http=HTTP_HOST to riak.RiakClient()
  So that setUpModule() and tearDownModule() will succeed
  to non-localhost addresses when running `python setup.py test`
Merge pull request #221 from basho/kr-explicitly-set-http-host

Update riak/tests/test_all.py so that non-local address test will be properly executed