Hadoop configuration proof of concept (DO NOT MERGE)

@e0d here is the ansible code we discussed. I wrote this a long time ago, really helped ramp me up on ansible.

Notable stuff in here:
* I was always testing this on a set of dedicated vagrant VMs. So it does scary stuff like clobber the /etc/hosts file.
* I don't remember what version of ansible I was running this stuff with... I think 1.4.4?
* There are some defaults for variables that look secure. They aren't and are not actually in use anywhere.
* I had half-extracted the security stuff, I don't think this is in a working state right now. It could also be vastly simplified if we removed all of the stuff related to kerberos and the "cdh-secure" tag.
* The "alternatives" module I actually got merged into ansible trunk a while ago, so we wouldn't actually need the custom module in the library.
* The way this is currently setup you can really only deploy a single hadoop cluster. The inventory isn't smart enough to distinguish between clusters.
* I have a bunch of other setup code for Hive etc, but this gives you the general idea.
* This is all using a fairly old version of cloudera hadoop.