Prefer connection to local host

[mciancio]

In the case you run your app on the same servers as the Riak cluster it would be nice, in order to improve performances, to give connection priority to the local host and connect to remote hosts only in case the the local one is down.
In other terms I want to suggest a "preferred node" to RiakClient. Do you think it is possible?

[georgepsarakis]

This seems possible and easy to implement in my opinion.
It would need the following modifications:

class RiakNode

• Add a weight property
• Add get_weight/set_weight getter/setter methods

method RiakClient._choose_node

• Add random.shuffle(good) (to avoid picking always the same node)
• Sort good list by weight
• Finaly select the node by taking the first element

[seancribbs]

@georgepsarakis Or we could just avoid that code path altogether when there's only one node. Either way, this will come after the next release. If you have the time to patch it, please send a PR.