Add initial host constraints

-Simplify host constraints and add V1 of code (uses separate hosts for
NN1, NN2, journal node, and data nodes).
-Remove resource code that’s currently being used for hostname
constraints
Please add a docblock comment to this and all other methods that return a null reference as part of their normal operation.  Better yet, make use of a wrapper monad. :smile: See http://www.codecommit.com/blog/scala/the-option-pattern